If she seriously needs medical attention, she would not get denied and be billed after the fact. If she has no earning power, she would likely qualify for Medicaid which would cover those expenses.

For incidental spending, I'd recommend a prepaid Visa or MC with a fixed balance. You can get them in any denomination and when it's gone, it's gone.

Maybe a few of those left in the hands of a responsible third party to whom she can go for help?

You can also set up a bank account into which you can transfer a cash allowance at your discretion. Take care to do it in person and to decline all offers of extension or overdraft protection.

If this is an issue for life, the court can appoint a guardian ad litem who will take on the responsibility of managing money for her.

I know that Walgreen's offers an Express Pay option on Rx where you set up a credit card used exclusively for your meds on pick-up. It does not cover anything else.