3 and half months, she is not having her periods. Due to some reasons she can't go for a test.

hi i had unprotected sex with my g.f in november 2012(date i dont remember but it was the mid of november) but i didn't cum inside her. She had her periods approximately after 10-12 days. Since then, its been 3 and half months, she is not having her periods. Due to some reasons she can't go for a test. Is she pregnant or is it just a irregular delay in her periods. Because i have heard that if the fertilization occurs(which according to my knowledge happens within 3-4 days), they don't get periods. Help me with this. She is 17.