So, does she ordinarily use condoms? Most sex workers do and if she does not, I'd consider not having her as your girlfriend anymore as that is irresponsible. If she does, great. Condoms will protect against HIV. The only risks to HIV are if someone has unprotected vaginal or anal sex or sharing IV drug needles. She had a test now and was negative. Great. BUT, if she'd had unprotected sex from the time two and a half weeks ago that you two had unprotected sex until the time of her test, it would have been too soon to test for HIV. The earliest one can should take a 4th generation Duo test is at 28 days after their last exposure. So, that 2.5 wee period is in question. She's on Prep though. That's prophylaxis and is quite effective so if she was on that, this should cover her from getting HIV and also you. But again, I hope she consistently and always uses condoms as that is not the only std she could acquire. You need to protect yourself in this situation.
If you had unprotected intercourse with your partner any time before 10-14 days before the undetected RNA PCR test, you are safe.
Your partner has made a wise choice to be on PrEP, it certainly minimises the probability of infection from unavoidable incidents. If you want to follow the guidelines of HIV testing, you can take a IV generation HIV test at 28 days from the date of your event, it is going to be negative.