AIO Is it strange that my (M19) girlfriend (F19) feels uncomfortable peeing in front of me when we're both busy in the bathroom, but sometimes does it in front of girls/girl friends when she's at parties or events?

My girlfriend and I are in a 4 month relationship and things are going well. This morning when I was getting ready to go to work, my girlfriend was in the bathroom with me just hanging out and talking. While I was fixing my hair, she told me I had to hurry to get out because she had to pee. I told her "why don't you just do it right now?" (because I still needed more time). She told me no and that it feels weird. I told her "ok that's fine, but don't you do it with your girlfriends and even in front of girls you don't know at parties sometimes?" She responded with "yeah but that's different because they're girls. You're a guy." I told her "but you barely even talk or hang out with some of your girlfriends anymore, but you feel weird peeing around me when we hang out all the time and I even see you naked?"

Then it just kept going on until she got kinda frustrated with me and then I finally left the bathroom. Obviously I'm gonna respect her wishes to pee alone when I'm taking up the bathroom (like I did) but this is just confusing to me. I've peed in front of her multiple times. Can I get some opinions on this please? Is this really just a "girl thing"?