[Daring Scylla]

first of all, I'm REALLY sorry that happened to you. I wish Steam were on to advise you because she could write the BOOK on crazy moms who don’t respect your space or sketchbooks or scholarly chaos in your room.
first, your mum's going to get all up in your stuff. unless they have no cares for you at all that's how mothers work. its just in their BRAAAAAAINS. you need to get used to that.
second dont take it lying down. explain (NICELY!) that you like your personal space and it really drives you up the wall when people get in your stuff without asking. even if she's your mom, say that ANYONE going through your stuff drives you up the wall. try to phrase it so she specifically doesn't sound/feel like the problem so she won't get defense.
third - you might no like this. but. apologize. say you're sorry for saying the angry things you did, and hten explain to her what made you say them so she doesn't write it off as angst or some rubbish.
it's a tense situation to be sure, like. you need to have patience and consideration towards her feelings... and accept that she's going to be nosy and have bass-ackwards logic because she's your mum. Moms do that. and good luck.