Right now the amount needs to be negotiated and paid. If it's just $100 or what the vote is there and without causing more hard feelings it just needs to be taken care of. Yes even if you have to bite your tounge the whole time!
Make sure this is all documented also.
NEXT TIME! get it in writing that this a volunteer job and she is donating her time. If she doesn't want to, fine, Plan B.
Not really happy and feel this was dirty how this was turned on the PTO but all you can do now is chalk it up as "next time....."
Thinking for the Principal right now, I honsetly feel that he/she wanted to keep their employee happy and she much have complained. Just do right by her but make it clear if she is needed again that the PTO was asking for her time and energy as a parent NOT the school cook.
What do I think? This is just the reason why we don't use the school kitchen for anything. We have never been able to establish a volunteer or pro-bono work with the "Kitchen Manager". Sad but true.