Presumably she treats her patients as members of the family (6)
I believe the answer is:
sister
'family' is the definition.
(I know this)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for sister that I've seen before include "Close relation" , "of the same origin" , "Resist (anag) - nurse" , "Nurse, nun and sibling" , "Nurse, nun or relation" .)