I had to learn everything the hard way, when I was much older. I plan to give my boys some guidelines, including things like "don't kiss a girl unless you're prepared to be nice to her the next day at school, in front of your friends". I would try to find out if pictures were sent to any other phones.At this point, getting your daughter to talk to you may be more important than punishing her. You might need to do some damage control if the pictures were forwarded anywhere (and that might involve yet even more parents).
These kids just have NO CLUE of the kind of fire they might be playing with. Also, raising her up in a house of good morals always helps too so she'll have a good conscience. I had boyfriends I got close to and took inappropriate pix.
this was back in the day before we had cell phones, let alone ones with cameras.
We took them to Walgreen's and had them developed when we went to pick them up the manager came to see us. You don't know if anyone has forwarded them to other people.
It seems that some people who worked in the photo department were under 18 and she felt it was very wrong for us to expose these people to the photos we had taken. You don't know if they are on the internet right now. If you have younger children in the house, have her consider how she would feel if they saw the pix.
What I didn't realize is that forwarding "inappropriate pictures" can be labeled as passing pornography.