Sally’s moving through this person’s agency (6-6)
I believe the answer is:
change-ringer
'sally's moving through' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'person's agency' is the wordplay.
I cannot quite see how this works, but
'person' could be 'ringer' (ringer is a kind of person) and 'ringer' is found within the answer.
The remaining letters 'change' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'this' acts as a link.
(Another definition for change-ringer that I've seen is " One performing peal".)