AIO for distancing myself from my younger cousin because of her constant criticism ?

So, here’s my issue. I have a younger cousin who’s 16(F), and I’m 26(F). I really care about her, and I know that personality-wise we’re quite different, but that doesn’t stop us from having a good time together.

The problem is that, due to her young age, she uses a defense mechanism that’s starting to get to me and hurt me. She constantly criticizes what I do, makes negative comments about my boyfriend, and keeps comparing things by saying how her boyfriend is taller, more handsome, etc.

I’m confident in my choices, and I don’t doubt them. But the fact that she brings this up all the time is exhausting and makes it hard to enjoy spending time with her. Since she’s younger, I feel responsible for staying mature and not stooping to her level, but at the same time, it’s really frustrating.

Sometimes, when I’m not in a good mood, I can’t handle her remarks, and I end up canceling plans with her by saying I’m too tired. I’ve also talked to her about this several times, telling her that her comments make me uncomfortable, but nothing really changes.

What do you think? How can I handle this without letting it ruin our relationship?or am i just overthinking it?