Sex on period.

Alright, here is a sorta long story.
My best friend since 2nd grade began to have periods around 5th grade, they were never regular and about two weeks ago she was diagnosed with PCOS (polycystic ovarian syndrome) and was given 10 provera pills to cause her to have a period. She took the pills the same time every day for 10 days and four days later her period started, the second day of her period she went onto birth control (as the doctor told her to). Well, three days after being on birth control; her and her boyfriend had sex for the first time, unprotected and he never ejaculated. Is is possible for her to be pregnant?
Oh yeah, she was also still on her period, and still on her period the next day.

Thanks.