S.A.
I know that you may not want to hear this but it sounds like your real problem is with your Boyfriend - he is allowing his daughter to behave this way and it is likely that she did not get that way overnight. I don't know how long you have been dating him but it seems that he isn't willing to stand up for you or to correct her behavior. She would stop having her hand out if he never put anything in her hands to start with!
It may sound cold but how did she get to a point where she is without resources? Where is her Mother? Where are the boyfriends/babies Dads? Where is the rest of the family to help out? It is likely that her self-centered and obnoxious, immature behavior has made everyone else give up on her, which is sad but it is of her own making.
If you continue your relationship with this man then you are in for a long battle with this young woman and your boyfriend is the one who needs to take action before things can change.
Good luck.
blessings,
Stacy