Well, it doesn't matter what the reason is - it's a shit test, or it's just shit, or whatever - we know how to respond to this.
I think you're in a great situation. Make the most of this, use her to learn how to keep your cool and maintain the upper hand no matter what. Call her out on what she's doing wrong and it's impacts, in a very factual, impartial manner. Don't insult, and don't tell her what to do. If she picks on you for something innocent, just say "I don't think I deserved that, I was only trying to [state your intentions]." and then she continues and you say something like "Why is this a problem? I thought we were out to have fun?"
But those were very generic, so actually I'd love to hear some specific examples - please share

I would like to have a go at saying what I'd do in that situation, maybe it'll give you some ideas.
But until then, the main thing is you have to remain above it. Don't engage her on that level when she starts doing that shit. Don't defend yourself - say what she did was wrong, state a simple fact as to why, and then the discussion about it ends there. Say "I'm not debating it with you." or "I'm done talking about that." Or something. Because you're better than that. Sometimes you don't even have to react, you can pretend it never happened! She might be like "tuh, I can't believe you did/said that." and you just roll right into the next thing like you never heard her
