Actually, the fact that she chose that disguise proves the point of people who
accusepoint out that she was a casteist. First of all, she called Keechak a suta, but beyond that, she told Bhima that she'd rather die than be kicked by a suta. How is being kicked by a suta worse than, say, being kicked by Dushashan? Until one tosses in all the caste based baggage that comes w/ it? (Yeah, yeah, I know that casteism was the norm at the time, but that hardly disproves the assertion of those who point out that factoid about Draupadi)
Also, the reason she chose the sairandhri disguise was that nobody would suspect her of doing it, since everybody knew that she was otherwise too proud to do it. And the whole point of year 13 was to assume a disguise that no one would suspect. Duryodhan too might not have suspected it had it not been for the news that Keechak was killed b'cos he was enamored by a beautiful married woman, which could only have been Draupadi
1. Slight grammatical problem in what you said: she referred to Keechaka as THE sutha, not A sutha. One word makes a world of difference in interpretation. First is an identifier, second is a class.
2. She didn't say she would die rather than be kicked by a sutha. She said she would die if she got outraged raped by Keechaka. Not A sutha or THE sutha, but Keechaka. Before you ask why not the rest of the men in the world... since he was the only one trying to assault her, she named him. I would say 99.9999999% of sane women would do that rather than blanket the whole male half of humanity with accusation of being potential assaulter.
https://www.sacred-texts.com/hin/m04/m04021.htm
Hearing these words, Draupadi said, 'Unable, O Bhima, to bear my griefs, it is from grief alone that I have shed these tears. I do not censure Yudhishthira. Nor is there any use in dwelling on the past. O Bhima of mighty strength, come quickly forward to the work of the hour. O Bhima, Kaikeyi, jealous of my beauty, always pains me by her endeavours to prevent the king from taking a fancy to me. And understanding this disposition of hers, the wicked-souled Kichaka of immoral ways constantly solicits me himself. Angry with him for this, but then suppressing my wrath
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[paragraph continues] I answer that wretch deprived of sense by lust, saying, 'O Kichaka, protect thyself. I am the beloved queen and wife of five Gandharvas. Those heroes in wrath will slay thee that art so rash.' Thus addressed, Kichaka of wicked soul replied unto me, saying, 'I have not the least fear of the Gandharvas, O Sairindhri of sweet smiles. I will slay hundred thousand Gandharvas, encountering them in battle. Therefore, O timid one, do thou consent.' Hearing all this, I again addressed the lust-afflicted Suta, saying, 'Thou art no match for those illustrious Gandharvas. Of respectable percentage and good disposition, I ever adhere to virtue and never wish for the death of any one. It is for this that thou I vest, O Kichaka!' At this, that wight of wicked soul burst out into a loud laughter. And it came to pass that Kaikeyi previously urged by Kichaka, and moved by affection for her brother, and desirous of doing him a good turn, despatched me to him, saying 'Do thou, O Sairindhri, fetch wine from Kichaka's quarter's!' On beholding me the Suta's son at first addressed me in sweet words, and when that failed, he became exceedingly enraged, and intended to use violence. Understanding the purpose of the wicked Kichaka, I speedily rushed towards the place where the king was. Felling me on the ground the wretch then kicked me in the very presence of the king himself and before the eyes of Kanka and many others, including charioteers, and royal favourites, and elephant-riders, and citizens. I rebuked the king and Kanka again and again. The king, however, neither prevented Kichaka, nor inflicted any chastisement on him. The principal ally of king Virata in war, the cruel Kichaka reft of virtue is loved by both the king and the queen. O exalted one, brave, proud, sinful, adulterous, and engrossed in all objects of enjoyment, he earneth immense wealth (from the king), and robs the possessions of others even if they cry in distress. And he never walketh in the path of virtue, nor doth he any virtuous act. Of wicked soul, and vicious disposition, haughty and villainous, and always afflicted by the shafts of Kama, though repulsed repeatedly, if he sees me again, he will outrage me. I shall then surely renounce my life. Although striving to acquire virtue (on my death) your highly meritorious acts will come to naught. Ye that are now obeying your pledge, ye will lose your wife. By protecting, one's wife one's offspring are protected, and by protecting one's offspring, one's own self is protected. And it is because one begets one's own self in one's wife that the wife is called Jaya 1 by the wise. The husband also should be protected by the wife, thinking,--How else will he take his birth in my womb?--I have heard it from Brahmanas expounding the duties of the several orders that a Kshatriya hath no other duty than subduing enemies. Alas, Kichaka kicked me in the very presence of Yudhishthira the Just, and also of thyself, O Bhimasena of mighty strength. It was thou, O Bhima, that didst deliver me from the terrible Jatasura. It was thou also that with thy brothers didst vanquish Jayadratha. Do thou now slay this wretch also who hath
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insulted me. Presuming upon his being a favourite of the king, Kichaka, O Bharata, hath enhanced my woe. Do thou, therefore, smash this lustful wight even like an earthen pot dashed upon a stone. If, O Bharata, tomorrow's sun sheds his rays upon him who is the source of many griefs of mine, I shall, surely, mixing poison (with some drink), drink it up,--for I never shall yield to Kichaka. Far better it were, O Bhima, that I should die before thee.'
Here you go. She says he will outrage (assault) her. Wanting to die for being/before being assaulted (a 3rd time!) is NOT casteism. It is called trauma.
Those who hurl FALSE ACCUSATIONS need to read the para properly. She didn't want to get raped. Fancy that!
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Actually, she also wanted Dusshasana dead while she tried to talk Keechaka out of his stupidity. Dusshasana was after all a kshatriya. She also wanted Suyodhana and Shakuni dead, who again were kshatriyas. She also advised Bheema and Arjuna to kill Jayadratha - once again a kshatriya. See the commonality? All men who attacked/played a role in attacking her, regardless of what caste they belonged to.
https://www.sacred-texts.com/hin/m04/m04017.htm
"Draupadi said, 'What grief hath she not who hath Yudhishthira for her husband? Knowing all my griefs, why dost thou ask me? The Pratikamin dragged me to the court in the midst of an assembly of courtiers, calling me a slave. That grief, O Bharata, consumeth me. What other princess, save Draupadi, would live having suffered such intense misery? Who else, save myself, could bear such second insult as the wicked Saindhava offered me while residing in the forest? Who else of my position, save myself, could live, having been kicked by Kichaka in the very sight of the wicked king of the Matsyas? Of what value is life, O Bharata, when thou, O son of Kunti, dost not think me miserable, although I am afflicted with such woes? That vile and wicked wretch, O Bharata, known by the name of Kichaka, who is the brother-in-law of king Virata and the commander of his forces, every day, O tiger among men, addresses me who am residing in the palace as a Sairindhri, saying, 'Do thou become my wife.'--Thus solicited, O slayer of foes, by that wretch deserving to be slain, my heart is bursting like a fruit ripened in season. Censure thou that elder brother of thine addicted to execrable dice, through whose act alone I have been afflicted with such woe. Who else, save him that is a desperate gambler, would play, giving up kingdom and everything including even myself, in order to lead a life in the woods? If he had gambled morning and evening for many years together, staking nishkas by thousand and other kinds of substantial wealth, still his silver, and gold, and robes, and vehicles, and teams, and goats, and sheep, and multitudes of steeds and mares and mules would not have sustained any diminution. But now deprived of prosperity by the rivalry
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of dice, he sits dumb like a fool, reflecting on his own misdeeds.
Somehow, those who ACCUSE Panchali of being casteist conveniently forget THIS factoid. 
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Once again, there remains the inconvenient fact sutha was not low caste, merely intercaste between Kshatriya father and brahmana mother.
The other inconvivenient problem is that while Panchali's motives are pure conjecture on your part, Karna's tirade against lower castes is well-documented in his conversation with Shalya.
The last para in quoted post as I said is pure conjecture. You don't know that was her motive. Plus, even her enemies conceded she worked day and night serving everyone in the kingdom. If anyone considered sutha as lower caste (which they were not), casteism is not something you conveniently forget while serving people, esp a sutha queen. She had no problems waiting on Sudeshna but had a problem being kicked by her brother and threatened with sexual assault. Every domestic helper in India would agree Panchali had the right to object.
On that note: @red. Citation, please. Let's see where everyone knew she was too proud to be identified as lower caste.
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I want to leave this information here for any lurkers stumbling upon FALSE CLAIMS of casteism thrown on a woman for not wanting to be assaulted.