Probably because she thought that maybe they can forget their past and at least be cordial with each other. Little did she know that gandagi ka box khulne waala hain. That ganda box will always haunt her for the rest of her life. Gandi naali ka keeda shukla
I brought up Rashami because SHE made the decision in the beginning to make Sidharth her kitchen partner. Not the other way around.
But yes if they hate each other so much, why did they go hand in hand?