Hi, There is a chance that she could be pregnant but it is unlikely as most people ovulate about 2 weeks after they have had their period which is when you can get pregnant. I wouldn't worry to much as the chances are very slim and even if you get a test it would not show up until she has missed her next period. Good luck and hope this helps xx
Take her to the local GUM clinic to have a chat with them - pregnancy is not the only worry here. Plenty of nasty STD out and about, even when you are only 15 and it's your first time(s). Has she been vaccinated for HPV?