She had to reform impetuous people (8)
I believe the answer is:
hotheads
'impetuous people' is the definition.
(I've seen this in another clue)
'she had to reform' is the wordplay.
'reform' indicates an anagram (letters in a new form).
'she'+'had'+'to'='shehadto'
'shehadto' anagrammed gives 'HOTHEADS'.
(Other definitions for hotheads that I've seen before include "Impetuous people with fiery temperaments" , "Working together" , "like a sound parachutist?" , "Impetuous folk" , "They don't think" .)