Hi,

It is unlikely that she is pregnant if she has had her periods.

Condom failure is fairly common cause of pregnancy and precautions need to be taken to prevent it. Condom failure usually occur due to condom tear .This occurs either due to inferior quality of condom or due to insufficient lubrication. Both these problems need to be addressed to prevent future tear of condom. As in your case, she had periods 15 days later, it is unlikely that she is pregnant although there is a very small chance that it was implantation bleeding.

I would recommend the following-

1)Take another urine pregnancy test to confirm that you are not pregnant. It may also help, if you are very anxious, to take an ultrasonography of abdomen.

2)make sure that you use good quality condoms in the future that do no tear easily. It's also important to wear the condom properly to prevent tear.

3)If she is not properly lubricated I would recommend the use of lubricant gels to decrease discomfort and condom tear.

4)Always use protection and follow safe sexual practices.

Thank you.