There is really not enough information in your post for us to make any kind of reliable guess, and at any rate, it's not possible or responsible for anyone to diagnose on a forum, unless they are a medical professional.
It would be a good idea for your friend to go to her doctor and get her blister looked at, if she's worried about it. She can get a blood test to determine if she has antibodies to HSV, though this will not tell her where she has it if she has it.
edit:
the spot pretty much looks the same as it did 6 days ago. It hasn't changed much.