Mum sleeping in my room

I’m a 15 yr old girl, and my mum comes to sleep in me or my brother (17) room literally every other day. It’s because my dad snores really loud, and she can’t sleep properly. Me and my brother always argue about it, and then she gets upset about it, saying we are selfish and ungrateful. We both want personal space, but every time we voice it she gets mad, saying she paid for all our stuff, buys us things etc and this is how we repay her. My mum really is generous and does loads of work for us, and it makes me feel so guilty. I am I wrong? She sleeps on the couch and I know she dosen’t sleep well, and I feel so bad. As well as this, the next day she is always in a mood, waking us up early and glaring at us. What do I do?