That seems very fishy and I guess she means that she laughs at wrong things at the wrong time, and she's aware of that (as if you were holding in a laugh at a meme on Instagram Reels in school). If she told you that, I think that should be taken as a precaution instead of like a full blown offense. I wouldn't recommend wanting to spend your life with someone like that if she's obviously doing it on purpose but at the same time, I have no idea what your relationship with her is like. That's definitely a weird thing to say, though.