Instrument for changing her boot (7)
I believe the answer is:
theorbo
'instrument' is the definition.
(I've seen this before)
'changing her boot' is the wordplay.
'changing' indicates an anagram.
'her'+'boot'='herboot'
'herboot' anagrammed gives 'THEORBO'.
'for' is the link.
(Other definitions for theorbo that I've seen before include "Antique instrument" , "Large lute" , "Lute-like instrument; O bother (anag.)" , "... something large to play" , "Old music maker" .)