My guess is that if she received the service/treatment she is liable for the payment. Generally you are responsible for any medical services provided to you that your insurance doesn't cover.
If she paid a premium to Ohio State for the insurance (and they rescinded the insurance) she should be entitled to a refund from Ohio State for the premium.
The "pisser' is that doctors/hospitals/labs have a variety of rates for the same service. The amount that they amount that they would pay the insurance company (Ohio State insurance's rate) is a lot less than the amount that they charge an uninsured person. Since they "told her she was covered at the time" I would at least make sure that they are charging her the insurance rate vs. their uninsured person rate. They may be reluctant to reveal their pricing date; but the bottom line is: any medical bill is negotiable and just how bad do they want paid? They may claim that their "policy" is to not reduce a bill or negotiate: however, there are always exceptions to every "corporate policy".