sumi the defense lawyer?

ok i dont get why is sumi krishna's brother defending prem as the defense lawyer???why is she fighting against her brother who he is sister's husband just murdered i don't get it? what the hell does she know about what happened to nandani she just heard about what krishna did she see see it. the prosecutor yashwant is too strong and sumi just got a degree in law it doesnt make her a real lawyer. i don't know what the director is doing and i dont know what sumi is going to prove to the court about her brother?????? comments plz...........