The antibiotic would not change the test result, no.
You know, when you describe something as blisters, that worries me. Blisters are so classic for herpes but in your most recent post, it doesn’t really sound like she has water blisters on her thigh but rather something that might be blisters. This is difficult over the internet, I know.
It is also very difficult to assess her risk without knowing what kind of sexual contact EXACTLY she had. If she was the giver of oral sex to this person and got herpes from the contact, her symptoms would be oral, not genital. Symptoms show up where the contact was.
I feel pretty limited in how much more I can help you and your daughter without having more specific information. I don’t know if you and she can talk about these things this frankly and openly – not easy with a daughter, perhaps.