My girlfriend (23F) keeps making sexual comments to me (24F) about my brother

I’m just had surgery, and I’m unable to have sex for a month while I recover. My girlfriend has jokingly asked me if I’d give her a “pass” to sleep with other people while I’m healing. I told her no, and we moved on. Two days later, she asked me again if she could have a pass with X celebrity, or Y celebrity, and then my brother. This is not the first time she’s mentioned sex with my brother, and I have told her in the past to stop thirsting, and making sexual remarks. She insists she was talking purely hypothetically, and that he was the only family member of mine she knew. I told her that hypothetical or not, it’s still a sexual remark about my brother. It makes me uncomfortable and she needs to stop. Is there anything more I can say to establish this boundary or is it best to go with my gut and end the relationship?