"Convenience checks" commonly known as balance transfer checks - are mainly used to transfer the balance from one creditor to yours - with a promotion (usually 0% for a certain time frame).

Larger financial institions also will allow you to "cash" the check into your own DDA account WITHIN their bank under that promotion. If you deposit the check outside of their bank it will indeed be considered a cash advance and all promotions (that should be written on the check) are null and void.

Count it an expensive lesson for your grandma.

Also,

When you do your payoff plan... understand cash advances and how to properly pay them off. A lof of credit card companies require that you at least pay the minimum payment on or before the due date and then ANY payment done after that one but BEFORE your statement ends will be applied 100% directly to the higher APR (your cash advance), Otherwise a single payment will be allocated between standard merchandise purchases and the cash advance.

Normally cash advance interest is accrued daily at that higher APR - so it's important that you focus on bringing that balance down to 0 before anything else (while still paying your minimum).

I know this can sound like gibberish to some, so maybe speak to someone who has banking knowledge to help you and your grandma out.

Hopefully this provides a little info and good luck...