She is a HOE.
She doesn't have to live with OP brother. She CHOOSES prostitute herself for money. If anyone should be ashamed it's her. I looked at the first couple comments demonizing OP brother. No, fuck that. Sure he is an asshole, douche, whatever, but her choice, her life, her responsibilities.
I bet she thought it was going to be alright. Figured it would be a win/win. Turns out, she's ashamed for being a prostitute, and should be. Only one holding the blame should be the OP brother's roommate.