Why is my girlfriend bleeding qhwn she just got off her period and cramping?

Common. Sometimes periods last longer than usual. Sometimes there is a little extra blood that comes a few days after the actual period ends. Ibuprofen is great for cramping. If it persists then schedule an appointment.
This may be normal. The length of periods is variable. If it lasts longer than normal or there is a change in her pain she should call her doctor.