according to my POV:
i agree that tapasya was mislead but i don't think it's entirely ichcha's fault.
when tapasya was small it was nani who filled tapu's mind with hatred, ichcha was too small then to explain anything to tapu what was right and wrong, but divya and jogi were her parents and they should have concentrated more on tapasya
jab woh bade hue tho tapu ka mindset already banchuka tha, so howmuch ever ichcha explained it to taps she never listened.
when it comes to why ichcha doesn't expose what tapu does is because (i think):
1.when they were small , tapu left her in jungle, when jogi came to know about this he sent her to hostel. this didn't change her but her hatred towards ichcha increased. that's why maybe ichcha is scared that if she tells everyone the truth then tapu will become more angry on ichcha.
2. maybe she thought that by doing this she'll understand that she never wanted to hurt her , and loves her whole heartedly.
even now ichcha is not behaving rude with her because she still has the hope that she'll change
(i think, that's what she said in the interview)
ichcha always tried to change her , lekin background me nani hamesha uske kaan barti thi.