Many women report having their period while pregnant, but typically this is not the case. The reason why this cannot be is that pregnancyand menstruation cannot take place at the same time, by the very definition of the two. If you were pregnant and you began menstruating you would inevitably lose the pregnancy, or have a miscarriage. While you cannot have your period and continue to be pregnant at the same time you can experience vaginal bleeding and continue to be pregnant. It is often this vaginal bleeding that women believe is their menstrual cycle when it is not. Early pregnancy bleeding is not at all uncommon and many women report that they do bleed regularly during the early portion of their pregnancies. This is not at all a menstrual cycle though; it is usually referred to as early pregnancy bleeding. This bleeding is usually is due to hormonal changes and is not of the quantities of blood that a woman typically sees when having her normal menstrual period. Early pregnancy bleeding can vary in amounts from slight spotting to vaginal bleeding consistent with a menstrual cycle. Please make sure she goes to a doctor and has a test done so that you can then together decide which steps to take next. 

Also, I wanted to add this information since you mentioned that she was on the pill:

Getting pregnant while on the pill is often associated with bleeding during pregnancy that can be confused with a menstrual cycle. Many women who are on the pill have several bleeding episodes before they realize that something is not quite right. In cases like this a woman usually cannot accurately tell her doctor when her last real menstrual cycle was and an ultrasound is required to provide the mother and the doctor with an estimated due date.

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