Helen & Co changed level (7)
I believe the answer is:
echelon
'level' is the definition.
(I've seen this in another clue)
'helen co changed' is the wordplay.
'changed' indicates an anagram.
'helen'+'co'='helenco'
'helenco' is an anagram of 'ECHELON'.
(Other definitions for echelon that I've seen before include "Level or rank in a group" , "Rank - status" , "Body of troops arranged in a line" , "Grade or level" , "Ladder formation" .)