Maybe she keeps giving you more stash because you keep giving her gifts. That is what I would probably do.
If she says it is a gift, then take it as that, be gracious and let her know how much you appreciate it just by telling her.
You say you are a pastors wife, you can respect the desire to just be charitable and I suspect you would do the same for someone else if you could. You likely give to folks in other ways without expecting anything in return. Put her in your prayers, what better gift to give.