that's easy, sorta.
first off I would suggest you call and speak to them, if that doesn't seem to be getting anywhere: ask them for the phone number of the B.A.R. (bureau of automotive repair, 800-952-5210).
just asking them for the number should fill them with fear. if they so much as suggest that they don't have the number handy, remind them that it's the LAW that it MUST be displayed inside the customer waiting area of their shop.

bottom line- she didn't sign anything? no need to pay.

the deal is that the b.a.r. will assume the customer is in the right and the shop will have a very nasty time from there on out. even if the customer is in the wrong.

shops know this.

so why was the car in for service anyhow?

/shop owner.