My (20M) girlfriend (18F) keeps insulting me and my cousin (20F) but says she's joking. Am I ignoring red flags?

My girlfriend and I have been together since last summer, but problems started when I told her that I’m very close with my cousin (we grew up like siblings and spend time together with family).

She started saying our relationship was “weird,” and started to make jokes about incest which I ignored at first.

A few months later, my cousin invited me to the movies since her friends were busy. I said yes, told my girlfriend immediately, and suggested we all go together. She got upset, saying she felt like a “second option” and refused to come, saying it's a "bf/gf thing". I also couldn’t go with my cousin without it becoming a problem, so I ended up canceling.

After that she brought up breaking up, saying my closeness with my cousin stresses her out, can't focus on school and that she will find someone without close female relatives and ended with "we can be friends tho". I talked it through and we stayed together.

The next day, she came to my house and was talking with my mom. I was acting like I normally do around my family (goofy and joking around) and my gf was giving me the death stare all the time. She went home, texted me saying “why did you act like an autistic while I was talking to your mom? I thought you used your braincells. Imagine if u acted in front of my dad like this. Also I can’t be with someone who acts like that” and suggested a break.

We later reconnected, and I suggested she meet my cousin to clear things up. They actually got along well in person and my cousin really liked her.

But afterwards, my girlfriend texted me saying my cousin is “boring” and “depressive,” (even tho she clearly had fun with her) and that she is fat and she never got along with fat people. Sadly I didn’t defend my cousin since I didn’t want to escalate things :/

She also made a “joke” about how her brother has a talent for languages and is always helping their dad and I’m just laying in bed doing nothing all day. I got really mad and she just said “please don’t get mad I was just kidding haha I love you”

What’s also bothering me is that she still brings up the movie situation months later, even though I canceled and never went, and uses it against me despite me asking her to stop.

She still shows affection and we have fun together, but I feel drained and can’t get over the things she’s said

TL;DR: My girlfriend keeps criticizing my relationship with my cousin, insults both of us, and often dismisses it as "just a joke." I still care about her, but I'm emotionally drained and unsure if I'm ignoring major red flags.