Humans aren’t designed to contain the time vortex; it’s too powerful even for a Time Lord to handle, and yet Rose has absorbed it and is using it, disintegrating the Dalek fleet, saving the earth from invasion or destruction.
The Doctor draws it out of her, knowing it will trigger his regeneration, but that’s preferable to letting a naïve, idealistic young human woman burn from the inside out. She wouldn’t be here if not for him; he has to save her.
But she’s already used the vortex to do something terrible, bringing Jack back to life as a fixed point…