Well, firstly you may want to check with an attorney in your state to see if debts that are in her name are passed down to her heirs, many times they are not and the debt just ends.
Assuming that you must (or just want to) to pay the medical expenses, you can use an HSA to pay medical expenses of yourself, a spouse or a dependent, even if they have other insurance and aren't eligible to contribute to an HSA. The expense must be incurred after the HSA account was opened.
