How does Prue halliwell die off the cast of charmed?

The sources assasin shax is after a dr. the sisters are trying to protect while trying to protect him their secret is found out so they must turn back time to before that happens but since Leo & Pheobe are in the underworld when time rewinds when Shax attacks Leo isn't there to heal the girls so Prue either has severe bleeding brain damage or both & dies.