I am going to play devils' advocate here and I say that in plural because there are two of them involved: both Prateek and Paridhi. Was her lying to the family and causing a panic wrong? Yes, but does that make her selfish and uncaring? Not at all! If so, she would have hid it from Prateek also, to ensure that her plan succeeded. What's more, I know she lied but she lied in order to do things as rightly as she possibly could, that is, go to Mumbai with the IL's permission. In her mind, she chose the lesser of two evils. If she wanted, the film was hers. She had her mother's full support and she could have just signed it but she didn't. She wanted to do things right by her new family and her husband. In return, she got accusations of infidelity. In my view, Paridhi keeps trying to be selfish, because she really does want her dreams but her basic nature holds her back at the last minute and she ends up doing the right thing. The sad thing though, is that she is getting rewarded with nothing for doing the right thing and getting everything she wants when she lies, so she feels jaded and bitter about the way things work in the Scindia household, as she expressed to Prateek and Yash.
As to why she told such a big lie this time, it has a lot to do with who was there to see her upset after Aarti got to go instead of her: Bua. Paridhi is used to an environment at home where she is the centre of attention and everyone is focused on what she wants and her moods. Here, she is disoriented because nobody seems to notice of their own accord, that she is upset because they seem all too absorbed in their own issues. She doesn't understand how this joint family system works, and in her notion of marriage, she married Prateek and so is reticent to interact with the rest of the family on any serious level without him as a buffer. She has not learned, and has had nobody go guide her in the fact that she has to ask for help when she needs it and people will only be too happy to help her, something she was made aware of only after Yash explained it to her. So she was all ears for the one "insider" who seemed to care, Bua.
Paridhi already had a history of lies getting her what she wanted in this family, while the truth got her nowhere, so when Bua guided her to lie about her dream, she actually believed that this is how things worked and people got what they wanted in this house, though she was not too happy doing it herself. She did what she felt was needed in this context because she simply does not understand that she does not have to lie, she explained this pretty clearly to Aarti and Yash, and that is where Prateek' fault comes in.
He never took the time to make her understand the way his family worked or how he planned to go about securing her job, so she started giving him ultimatums from day one because she felt like she couldn't trust him. But unfortunately that very distrust s what caused him to stay away from her because she made him feel inadequate and small. Instead he went towards relationships that inflated his ego and made him feel like he was accomplishing great things: ie as cupid for Yash and Aarti. I wish Prateek had taken the time to explain to Paridhi who her friends are in the house, and not just who she should be afraid of. I wish he had told her that Yash might seem wrapped up in himself but that he always has a listening ear for her problems and is willing to help.
But here Prateek fell weak. He didn't want anyone to know he couldn't deal with his wife on his own, so he hid her problems and isolated her from the family but did not protect her so she got into feeling like she was always a part of the family's problems but they were not part of hers. Everyone assumed that Prateek and Paridhi were blissfully happy because Prateek didn't reveal anything and Paridhi went about doing the things she was told to uncomplainingly, like taking care of the kids when Aarti was working. She only complains to Prateek because she only feels like she knows him and I think that is the biggest unfairness from Prateek's side.
This got longer than I expected but I hope it makes some sense. Neither of them are selfish or bad people but they are driving each other to desperation, one by not communicating and one by wanting things only on her terms. Both of them need some guidance, reassurance and support, which I hope they now realise Yash and Aarti can give them.