Manager snoops on my computer?

Is it weird that I've caught my manager going through my computer multiple times now? Never in front of me, always when I'm around the corner and she thinks I can't see her. Then she acts all nervous and awkward when I come around. I have absolutely nothing to hide. She is not the big boss and isn't the one to pay me, but acts like I'm her cheating husband. I feel like she just doesn't like me and is looking for a reason to get me fired. I go on maternity leave soon and feel like 1. What's the point I'm leaving soon and 2. It's not even paid leave.

I understand employers can have access to your browsing history and emails, etc if they feel you've been up to no good. But to do that she'd need permission from my big boss and a good reason. So this snooping just seems bizarre and rude. I was in a meeting the other day, in a room where she thought I couldn't see her (but I clearly could) and I just watched her go through everything on my computer for like 20 minutes. I just sat their like wtf this is embarrassing for her.

She's a massive hypocrite as well. She spends all her time on social media while at work and I have literally never gone on social media on my computer at work (I don't really use social media), yet she claims I'm always doing it and tried to get me fired for it once, but couldn't.