State must act as she's in a mess (13)
I believe the answer is:
massachusetts
'state' is the definition.
(Massachusetts is an example)
'must act as she's in a mess' is the subsidiary indication.
'in a mess' indicates anagramming the letters.
'must'+'act'+'as'+'shes'='mustactasshes'
'mustactasshes' anagrammed gives 'massachusetts'.
(Other definitions for massachusetts that I've seen before include "Bay State" , "A NE US state" , "Harvard's state" , "US state, capital Boston" , "One of the original 13 US states" .)