I’m sorry about this new development.
Do you know any details about her sexual encounter? Was she the receiver of oral sex from this new person or did they just have intercourse? I took a quick look back and could not easily find a description of her sexual encounter. If she was the receiver of oral sex there is a chance she could have HSV 1 and the test did not pick it up.
My recommendation would be to go in right away to have the blisters swabbed while they are still blisters – like today. How big are the blisters? Can you describe them more fully to me? And where in the groin?