It does not sound like herpes to me. is she sexually active, do you know? Would you feel better if her pediatrician took a look at it?
Herpes would not show up on the back of both legs at the same time, no, not in a healthy teenager.
You are letting your fears get the best of your reason here. You did not infect your daughter. I’ve never ever seen this happen though I have seen so many parents who worry about this.
It isn’t appropriate for her to be tested at this point and I would not recommend that you do that.