If she is on the pill.. During the last cycle of her pills which are basically sugar pills. That is when she should be having her period. You don't say how long she has been taking the pill. If she is on the 28 cycle .. and on her sugar pills.. then every 28 days she will have her period. So if she started today.. then it is possible for another period again towards the end of next month too.
Also with her getting her period today.. Then the chances of her being pregnant would be very, very low.
But if the period doesn't seem to last long or is not her Norm- then she may want to follow up with a HPT in about a week.
Hope this helps. If you need anything else please feel free to ask.