She knows he left everything in search of her and suffered without her literally (obviously he has suffered more than her, she had her son Sumonto with her, a loving DG famiy- jhoota hi sahi, and all the riches).
She knows about his craving for a child and also know how much he wants to enjoy his fatherhood.
He had told her, he would turn an animal if she doesn't come to him, and he did.. she knows her husband does what he says.
Last but not the least, she knows he needs her.. more than anyone else.. (Mujhe teri bahut zaroorat hain Prachi- dialogue is evident of that, if she claims she didn't know it).
Leave all these "she knows" stuff apart.. She saw that Milind had decorated a room for them beautifully, just like he had done when his memory was back or when it was their first monthly anniversary of their second marriage.
So, there is a Milind, who hasn't changed a bit when it comes to Prachi. Now that she saw him going to the extreme of self destruction, isn't it time that she learns she should support reality and not fakings?
I hope tomorrow we will see a bit of our Prachi back and Panchi got burnt in the fire.