I used to do what your girlfriend did. Set 'traps' exactly like that. If my then-boyfriend (now husband) mentioned casually he would do something, I would just wait for him to forget and not bring it up so I could take it out on him afterwards as 'proof' that he didn't care about me. Sometimes I'd kind of 'encourage' events so that he could 'fail' my stupid 'tests'. Or I'd pick apart things he said to make them sound much worse than what was intended. I was really awful and ridiculous. I didn't know what I was doing was abusive, I thought I was just trying to figure out how much he cared about me. If he cared, he'd read my mind and pass all my tests, right? Ugh.

The only reason I stopped doing it was because he figured me out fast and then wouldn't put up with my crap. As soon as I'd start up, he'd tell me to stop it (often in not very kind words) and leave. He never gave into my game and apologized or tried to fix his 'mistake'. He told me to get therapy if I wasn't willing to work on changing this immediately. It was hard for me, but I needed the tough love. I used to drive myself crazy with thoughts about how someone didn't really care for me because they failed to do/or did something trivial, and I don't anymore. I feel secure and cared for, and we never have these fights anymore, in fact we don't fight much at all. A few weeks ago we went out for Chinese and when leaving, I dropped my fortune cookie. I doubt he even saw, and he ate his. The old me would have cycled over this thought for days that because he didn't see me drop my cookie and offer me his, it meant he didn't really love me. And I would have taken it out on him. I now know this thinking is insane, it's so awful and abusive. But I'm sure this is how your girlfriend thinks.

So in summary, you need to not allow this crazy thinking and abuse. You tell her to "Stop, I'm not putting up with this." Don't argue with her about why she's wrong because she won't see it, and she'll use whatever you say as further 'proof' of how awful you are. Just tell her to stop, I'm not taking your shit, and leave long enough for her to cool down and reach out with an apology. It's like training. Eventually she will know if she acts out, she won't get the attention she is seeking. She'll be left alone. She'll think twice before doing her shit. And once she changes her behavior, her internal thought process will follow. She will realize she was wrong. She will think, "Why in the hell did I ever used to let myself get so upset at pretty much nothing??"