OK first of all, great discussion, and secondly if u accept she is physico then she don't deserve punishment but she needs treatment, and since it's Rajshri, there is a high chance Sandy will be forgiven at some point t and she will turn good😆, same goes to all negative ppl that we hate till now, Rajshri will make them all good by the middle to end of the show and if needed introduce new evil ppl and then cure them too by the end..in short Rajshri will give a happy ending with everyone leaving happily...
Ok so this is what might happened...
Sandy might have lost her family in an accident, now this is either done by Nirnala or happened while save Nirmala, either way Nirmala is the reason..This is why Sandy was brought to Chauhan house, she was happy and was ruling the house until Karan was born and she felt her importance in the family was less, because of him, and I also feel Kabir was her son's name and since everyone rejected the name she was even furious, and from then she decided to ruin everyone's life, she didn't attack Karan only..she broke Nirmala's confidence, she spoiled NK, and she broke relations between NK, Dadu and NK, Nirmala,, she spoiled Khyati and also created difference between brothers., now she needed a strong reason to keep thin gs messed up, and she feels Karan is the reason for her sorrow so she went an extra mile and affected him the most, either that or Kunal was already grown so it was difficult to break mentally, so she chose Karan and started breaking him from an baby...and Karan's condition was reason no one was happy...
so what I am saying Sandy is physico, and she wants to destroy everyone, now effecting Karan can either have a motive or it can be just she needed some one and Karan was easiest target...
now as for Naina, well this is how I feel things are gonna go, she will be emotional, and show sympathy for Sandy and so insted of trying to fight her, she will just focused on curing Karan just like Meghna will make Nirmala better incited of fighting NK, lol Rajshri loves peace, and humanity, so they will just show defeating evil with goodness and forgiveness...
just hope she don't get blind and let her guards down, she needs to cure Sandy, and protect Karan from her..