Telling my mum to stop wearing my clothes

My mum (52F) has recently lost a lot of weight and has become more confident in wearing nicer clothes. So much to the point she goes into my closet (20F) and takes out whatever she wants to wear and rubs it in my face that we are the same size.

I then proceed to say that we are not the same size and she gets really defensive and goes on and on about how we are and how we can fit into the same size clothes. But she doesn't realise her bust is 5x the size of mine therefore stretching all my tops.

I've eventually gotten very annoyed and it has upset me that she's somehow getting a kick out of being the same size as me as i've struggled with my weight my entire life.

Every time she comes into my room and i say no she responds with "it's my room". But the part which really got to me is when i said we are not the same size she proceeded to get a tape measure and started comparing our measurements which really puzzled me.

I grew up as a fat kid but she helped me lose the weight rapidly before i started high school, mostly by bullying me and telling me i wouldn't get a boyfriend being that big. And every time she sees me eating she asks "how's your diet going" or says "eating is cheating".

The point is i think this goes deeper than just wearing my clothes it's more of a haha i'm the same size as you and I'm 50! It's almost like a competition to her.