Thanks for the idea, Cherryblossom! I can't fix a lock since it's my house. I didn't want to just throw away other people's suggestions though. I will definitely use some sort of doorstopper. My mom can go to hell or learn what she needs to get before I go in there!
The norm in my family is no secrets, no privacy. My father used to read my computer stuff, right down to my IM conversations. (Now he doesn't, thank god.) My parents go to the bathroom with the door open, walk around naked, and don't make any attempt to hide their personal lives. (I've caught them both cheating.) It forces me into an awkward position between being open and having to hide things about myself from them. They don't believe my PTSD or any of the abuse in the slightest, so I have to hide these things. Therefore my computer stuff is sensitive since I acknowledge these things on here (like I am now.) But now even if my father did want to snoop around my computer, he couldn't. I turn the monitor off and use screen reader on earphones when he's home. And I turn screen reader off when I'm not at my computer (and he doesn't know how to turn it on, nor does he know how to turn the monitor on so he can't find out). It's made me very paranoid about how I use my computer. I always make sure there's a wall behind me and I use my earphones to keep everything private.