How to discreetly sabotage somebdy?

Okay, so my Mum's friend's daughter from Australia came to stay with us for ' a couple of days' she has ended up staying for over three months. My Mum's friend's apartment upstairs is empty so Leanne ( the woman) stays up there. But she comes down everyday and watches tv, so I can't watch what I want to, and sits on our couch with her big fat bum taking up all the space, so I have to sit on the beanbag. She eats our dinner every night, asks for breakfast and lunch, she doesn't leave till midnight on a school night. When I call my mum, Leanne walks in to my room. When my Mum and I were going to the movies together, she asked to come and talked through the whole movie! I've tried everything from telling my Mum Leanne has said bad stuff about her, telling my mum that Leanne has looked through her folders. I hate her,I want my privacy back, I can't STAND her and want to sabotage her discreetly but awfully, without my mum or her noticing. Ideas anyone??