If either of you is a minor, you are receiving and she is engaging in child porn. Yikes.
If not, it is a private photo between you two. But, I often wonder how private photo transmissions really are.
Have you seen the Victoria Secret fashion show on national TV. They show lots of skin there and ain't no one getting in trouble for that.
EDIT: OH, you are BOTH minors. Whelp, demand that she cut the crap or you can both be arrested and then guess what happens? You have to file on the SEXUAL OFFENDER web site in your area. This is nothing to play around with, you know.
My brother got caught taking a leak in the bushes at the beach. Some young girl saw his back and his stream of urine, not even his penis, and the police were called. He was arrested for indecent exposure and he is on the sexual offenders list. This is serious stuff you are messing with here. STOP IT TODAY.