She can buy 1x500 mile upgrade sticker. Don't need to have status. Cost should be $30 if you can mail in the voucher for this (I don't know) or $35 at the airport.

Whatever you do, you want to deal with this fast so you can MAIL the voucher in. If you do it at the airport, she will have an extra $30 charge (I assume your mom is NOT EXP). I do not know if this $30 charge applies for purchasing 1 500 mile sticker.

Alternately, if you need to do ticketing at the airport, your mom could buy this throwaway ticket in the name of an EXP. I'm sure a friendly FTer would help you out with this.