How to put my foot down!

So my parents live in a duplex my uncle owns and the bottom apartment is the only thing we can afford for a while until I go to police academy. Some lady my mom helped move from Canada is living there but it's supposed to be TEMPORARLY! My mom is now saying the lady is being picky with the houses and apartments that she needs to apply at to leave and get her own place so she might be there when we move back in May and my mom has this ghetto money making idea saying that she can rent a room out of our apartment and live with us. I say F* that! I want our house to ourself and our privacy. I don't know this lady!!! What can I do when we show up in May and I'm 8 months prego with that lady still there?! My parents knew our move back date since we moved to Cali 4 yrs ago! So this isn't news.