sounds like sour grapes...if the letter did not say specifically what it was being spent on I would stand your ground. I have something like this going on in my group right now that we are waiting the results for! Tell her you are sorry that she feels that the money isn't benifiting the school the way she would like...
Our President quit in Feb. She has done nothing but bad talk the PTO since. While Prez she donated $75 to an "opt-out" of fundraising that she sent out while President. She now wants the money back because we are not using the funds the way she wanted to. It doesn't say anything in our by-laws about Refunds! The letter said the money would go towards PTO operating expenses, not towards anything specific.