It is commendable idea. If you want to nourish only out of Islamic sympathy, affinity as well as for the sake of Allah then Almighty Allah has promised that such a person shall go to paradise who nourishes an orphan. Such person shall also be close to the holy Prophet Muhammad (صلي الله عليه وسلم). It is an act of high reward. If your bhabhi does not want to stay with you then how would she bring up the child?
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband