I too do not see why agency is the answer, but none of the other 12 which Wordfinder has fit the clue either:
agence, aleece, alerce, amedco, amerce, amerco, amexco, aneuch, aperch, apercu, areach, avemco
Thank you all. It would seem that "agency" is correct - in that an agency is instrumental in helping one do something but it is a somewhat clumsy clue.