Pet damaged her mast (7)
I believe the answer is:
hamster
'pet' is the definition.
(I've seen this before)
'damaged her mast' is the wordplay.
'damaged' indicates an anagram.
'her'+'mast'='hermast'
'hermast' anagrammed gives 'HAMSTER'.
(Other definitions for hamster that I've seen before include "Small pet rodent with pouched cheeks" , "Animal" , "Common pet rodent" , "Pet rodent, may be golden" , "Rodent with large cheek pouches" .)