Ok, so what happened was, after Ira gets seriously injured on her head from some accident, Revathi and Devki begin to brain wash Isha that she wont be able to take care of Ira if Ira was to get hurt in the future again. This time, Aunt Indrani paid for Ira's operation but maybe next time Ira gets hurt, Aunt Indrani wont be able to... SOOO Isha, decides that she should make Aunt Indrani adopt Ira. Isha knows that Ira wont leave her so she begins to make ira hate her. After Ira is discharged she goes to Isha, but Isha says things like:
-your always bothering me
-you never let me how my own childhood
-i always gave up my meals for you
-see kuhu? shes 1000 times better than you
-if you went away, it would make me really happy
However, Ira is unnaffected by this for a while, but Aunt Indrani takes her to mumbai or delhi (forgot which) for a while and when she comes back, she wants to hug Isha, but Isha says no, and that shes very busy (I was raining tears as that time DX)
But the biggest event that led Ira to absolutely hate Isha, was when Revathi and Devki put Sanskar Orphanage on fire. Isha who was walking back to the orphanage, sees that its on fire, but doesnt see Ira outside. She screams ira and runs in. When she gets in, Ira is crying and Kuhu is on the other side, so now Isha must decide who to save, because she can only save one. Then she sees Sam coming to save Ira, so she decides if Sam is saving Ira, she can save Kuhu, so Isha goes to save Kuhu, but Ira mistakes it as, Isha doesnt want to save her, because Isha hates her. (This is also why Ira HATES Kuhu). Even after everyone is rescued, Isha only asks Kuhu how she is doing, and not Ira, so Ira's getting really mad.
Finally after everything settles down and a few days pass, Ira comes to visit the orphanage, and Isha decided what she did to Ira was wrong, but it was too late, for Ira severed all relationship with Isha. (I couldve died from crying at this part DX) So that's how Ira hates Isha. But Ira's so stupid she should know that her sister gave up everything just so she could have a good life, but she doesn't know, and she wont let Sam explain.