Don't go along with errant sister (6)
I believe the answer is:
resist
'don't go along' is the definition.
I can't tell whether this defines the answer.
'errant sister' is the wordplay.
'errant' is an anagram indicator (errant can mean travelling or straying).
'sister' with letters rearranged gives 'RESIST'.
'with' is the link.
Can you help me to learn more?
(Other definitions for resist that I've seen before include "Refuse to give in to" , "Put up opposition, defy" , "Fight back" , "Stand firm against" , "Stand up to, fight against" .)