In answer to your question about your girlfriend having a period for two weeks, then stopping and reoccurring again some days later, there are a few medical reasons for this.
Firstly, could she be pregnant? When a woman is pregnant, sometimes she may experience 'spotting' which can sometimes be confused with a period, but is not a period.
Why your girlfriend's period might have stopped & then started again:
This is perfectly normal and safe during pregnancy. This type of bleeding can start and stop at random intervals, which could be the type of bleeding your girlfriend was experiencing.
Spotting is usually much lighter than a regular period. If she hasn't yet, it would be worthwhile for her to take a pregnancy test, then seeking advice from a medical professional.
If the period stops all together for a period of time (amenorrhoea), this is typically the main indicator of pregnancy. There are other reasons that could contribute to a stopped period, including stress, weight loss and hormonal problems which can cause a period to function out of synch.
Irregular periods & other problems
If your girlfriend experiences vaginal bleeding outside of her regular period, it is vital that she sees a doctor. There are several different causes for this, but ultimately it is necessary for her to speak with a medical professional who can assess all of her symptoms and provide her with an appropriate diagnosis.
Having irregular periods is also an indicator that you may not be ovulating each month, due to a hormonal imbalance.
This can be fairly common in the lead up to menopause, but somewhat uncommon in younger women. Once again, it is vital that under such circumstances, your girlfriend seeks professional medical help.