My girlfriend is currently on her period (heavy) but is having food cravings, stronger appetite, and stomach aches. could she be pregnant?

No: If a woman has a menstrual period, she is not pregnant. The process of the flow removes the contents of the uterus. That's what it is. If a fertilized egg has implanted itself those contents are needed to support it - they do not flow out. Any egg that is not implanted is carried out along with the flow. The symptoms are not from being pregnant. Do a test if you're not convinced. Best!