I wouldn't bother telling the agency. Just do your summer, earn some money then give her 2 wks notice. Be firm and tell her that it's too far to travel for bookings, but when you're in the area you'll let her know.
Then if you do want to continue when you're in uni, find somewhere a bit closer. There are loads of agencies and if you only want to do a bit of work, the indi route may be a more viable option.
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