She Secretly Rips On Me To The Seniors

I started dating Jenna last summer cos we worked the same summer job. She is a senior in high school. I'm only a freshman. She's really sweet to me and we have a great time together when we're alone. But when we get around her friends that are seniors she picks on me. Here's what she does.

Yeah if he could drive anywhere.
She laughs about me not being able to grow a beard.
She laughs that I'm smaller than most of her friends.
If they say something about me she laughs with them instead of defending me.

If she really cares why isn't she on my side? I tell her it upsets me and she shrugs it off or tells me about her reputation. I mean she's dating me. Why date me if I hurt your rep?

Please tell her to start backing me up!