To answer your question about how to approach this:
APPROACH BOLDLY.
Without fear. With no questions asked. With no discussion. With no leniency. Without anger, with politeness, yes, but with no flinching or wishy-washy words.
You calmly say to your daughter: "You have disobeyed the rules about not taking and not sending selfies. You knew the rule and you chose to ignore it. So now you will not have access to a camera, a webcam, a smartphone, or anything else that can take and send photos."
Make sure at this point that she doesn't have a laptop with a webcam, or an iPad, or anything similar.
Then you say "It was a simple and important rule. You'll have to earn the trust back that you broke. For the next [six months, or year, or till the end of the school year], you will not have a smartphone."
It's important that you remain calm, that you keep this about obeying rules and about being trustworthy and reliable. If you let the conversation go to the dangers of selfies, it will just descend into something that she and you already know. When she is getting her learner's permit in a couple of years, I'm sure she will know in her brain about the potential dangers of driving (too fast, driving while texting, etc) but you will establish rules for using the car. No passengers at first. No driving after dark for the first few weeks, etc. She needs to learn NOW that there are two sets of rules that will be enforced. The first is established by the police department, like speed limits and stopping at red lights, etc. The second is established by the parents who own the car. And those vary from family to family, depending on circumstances. Some families forbid the use of the car except to go to work and school. Some limit passengers. Some forbid passengers. Some install apps that limit radio volume and speed. If your daughter can't follow the smartphone rules, and if you don't act now, you will have a rough road ahead.
If she must have a phone because she babysits or goes to team events at school, you get her the kind that just makes and takes calls.
If she balks at this, you simply remove all phone privileges. Password-protect your WiFi.
Approach this seriously, calmly, and without hesitation. Don't allow her to beg for one more chance.