period 2 months late!!!!!!

OK, so we are young, and imma tell u now that she is not normal with her periods but times like this still scare me. its been about a lil more than 2 months since her last period. she has been bloated for some time now and her breasts are sort of tender, sometimes more than other times. she said they tend to hurt more at night than anything. she also says that she feels moody sometimes but again thats also a symptom of pms. she has/is recovering from having a uti. we have taken 2 home pregnancy tests and they were both first responses and they both said negative so that eased my mind a bit. but im still scared that she has missed 2 months already. her stomach doesnt seem bigger too much, but it does look bloated like she says. is this normal? she is also kind of active, she used to be realy active and she played polo last year and she is 17. She has also been stressed with school and with me going to college and stuff as that. please help me and ease my mind.