Hat's crumpled -- old lady makes a complaint (6)
I believe the answer is:
asthma
'a complaint' is the definition.
(asthma is a kind of disease)
'hat's crumpled old lady' is the wordplay.
'crumpled' indicates an anagram.
'old lady' becomes 'ma'.
'hats' anagrammed gives 'asth'.
'asth'+'ma'='ASTHMA'
'makes' is the link.
(Other definitions for asthma that I've seen before include "Mat has a breathing disorder" , "Cause of breathing difficulty" , "Breathing illness" , "Chronic breathing condition" , "Respiratory condition" .)