I am only adding my two cents for whatever it is worth.
I'm not saying it's right, I'm not saying it's wrong, but when I saw the words: "severe breach of trust and safety" I kind of wondered if there is more that you haven't told us.
Because if this was the first time, and if your daughter walked home, and it took her an hour and she didn't call you, but she let you know when she got home (or if you had asked and she told you then) what she was doing, who she was with, and that she was sorry for being late: I would say thank you, and talk to her about how worried you were and your concerns. And just have an adult discussion.
If your daughter was into drugs or alcohol or a bad group of kids I would worry, but if it's just hanging with kids at school I wouldn't have a problem with that as long as they are a good group of kids. You have to trust that you have instilled the differences between right and wrong in your children and trust that.
If there was a problem with the boyfriend and sex issues, I would say there would be a problem, BIG PROBLEM, but if it's not then why worry.
If you lived in a bad neighborhood, I would be worried.
I guess for me or anyone to offer you an opinion on a punishment, we really would need to know about the situation. Every child is different. Every parent has different rules. Every environment is different.
My advice is to look into your heart and ask yourself if "YOU" did what your daughter did, truly in your heart, how would you have wanted "your" mom to handle the situation with "you"..............Then take your own advice.
I can only share with you that these years are the hardest on these kids especially these days with all the electronics, the peer pressure, the internet, etc. there are so many choices kids have. Not like in my day, where there were no cell phones, or internet. We all talked to each other.
I am not making excuses for them, I have only seen what we've gone through with our children. Age 15 was my nightmare.
13 is such a hard age for kids. They are trying to find their identity and trying to break that "kid" label.
Our daughter wasn't into boys until she was 15, so 13 for me is kind of a young age to be dating. We didn't allow dating until she was 15.
But, I know that if you ask yourself that question, you'll answer your own question. Hope that helps.