If i understood you correctly, she got a negative p24 post 19 days from her exposure?
That is a great news because p24 would almost always peak at 14 - 21 days post exposure. If she was infected, it would have been detected. I would say every thing is in ypur favor right now. Though she would still have to test at 28 days with a IVGen or a standard HIV tes at 6 weeks for a conclusive result.
Also the above testing recommendation applies for you. You are going to be okay, i believe. Good luck.
If you speculate HIV for some reason for this unprotected exposure. You would need to test. The soonest you could test is at 28 days with a IV gen HIV test. Or any standard AB test post 42 days.
I suggest you to also think rationally, not every one is HIV positive. Sex is a great thing, people have it all the time. Don't get in to symptom searching and overanalyzing your body, just take a test and put this behind you. Good luck.
If she had sex with the guy 4 days before she had sex with u, u had no risk because it is too early.
However, such things are very difficult to predict.
Since u had unprotected sex, i assume vaginal sex, then i advice u go at hiv test at one month time