She can't possibly punish (7)
I believe the answer is:
chasten
'punish' is the definition.
(chasten could historically mean to punish)
'she can't possibly' is the wordplay.
'possibly' indicates an anagram.
'she'+'cant'='shecant'
'shecant' with letters rearranged gives 'CHASTEN'.
(Other definitions for chasten that I've seen before include "Castigate or punish" , "Subdue the pride of, discipline" , "Censure severely" , "Humble" , "Moderate" .)