We have treated for scabies twice my 6yr old has a puss filled blister on her hand does that mean she is still infected ?

See below: If only one blister, unlikely. She should be evaluated.

Not necessarily: Many times bacteria can get into the disrupted skin layers of a kid with scabies & produce a localized bacterial infection. This should be evaluated. We often see it take 6 weeks or more for the skin to calm down after a significant scabies infection, but it also can recur after re-exposure or emergence from an untreated site.