Waitress finds mother in rabid form (7)
I believe the answer is:
barmaid
'waitress' is the definition.
(thesaurus)
'mother in rabid form' is the wordplay.
'mother' becomes 'ma' (ma is a kind of mother).
'in' is an insertion indicator.
'form' is an anagram indicator.
'rabid' with letters rearranged gives 'barid'.
'ma' put into 'barid' is 'BARMAID'.
'finds' is the link.
(Other definitions for barmaid that I've seen before include "attendant" , "Pub employee" , "Local girl" , "She serves drinks" , "serving lady" .)