Careless or else she'd changed (8)
I believe the answer is:
heedless
'careless' is the definition.
(similar in meaning)
'else she'd changed' is the wordplay.
'changed' indicates an anagram.
'else'+'shed'='elseshed'
'elseshed' anagrammed gives 'HEEDLESS'.
'or' acts as a link.
(Other definitions for heedless that I've seen before include "Incautious" , "Paying no attention, to advice or danger" , "Inattentive, unmindful" , "Rash" , "Showing a lack of care or attention" .)