Stands up to unruly sisters (7)
I believe the answer is:
resists
'stands up to' is the definition.
(I've seen this in another clue)
'unruly sisters' is the wordplay.
'unruly' is an anagram indicator.
'sisters' anagrammed gives 'RESISTS'.
(Other definitions for resists that I've seen before include "Fights back" , "Defends" , "Is reluctant" , "Opposes, puts up fight" , "Sisters (anag.)" .)