...why would they be hurting? She had her last period a little over a week ago, &she complains that her breasts are throbbing day and night... What could it be?
Take a pregnancy test, JUST to make sure she's not pregnant. That would probably take your mine at ease. Breasts throbbing happens to EVERY woman at least once in awhile...
If it was a heavy period, or a normal period for you grilfriend she won't be pregnant. Breast pain happens at certain times of the month for girls, its different for them all, it could happen a week before her period or a week after.
I'd do a pregnancy test to put your mind at rest but also be aware sore breasts can happen every month for women.