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 can mean mother).
'in' is an insertion indicator.
'form' indicates an anagram (a different form of the same letters).
'rabid' anagrammed gives 'barid'.
'ma' put inside 'barid' is 'BARMAID'.
'finds' acts as a link.
(Other definitions for barmaid that I've seen before include "attendant" , "Pub employee" , "Local girl" , "She serves drinks" , "serving lady" .)