OMG, I know exactly what you mean we have one of those parents also. She literally makes my stomach turns upside down in disgust. It really makes me not wanting to be a part of the PTA this year. But I read something so cute on this message board that I have to post it in my mind, on my forehead and in my car to keep me from going off on her with her negativity. It reads: PEOPLE HAVE THE RIGHT TO BE STUPID, BUT SOME ABUSE THEIR PRIVILEGES. If that statement ain't the truth. So if I decide to be a part of the group this year I will have it in my mind thinking of her especially.
I try to ignore her at every given moment and you know it has been working for me. If she says something that ignorant, I look at her as if she's transparent to me. I don't even reply. I feel I have to much to loose to come down on her level. But try ignoring the nut and put her in the hands of the squirrel who is looking for a nut to crack!

Oh I so have to use this on one of my parents who I have had to deal with at meetings. She is turning alot of people away and she has no idea how she comes off to anyone else. Very good line.

Saleing--that's a nice approach actually. Especially "you can't possibly imagine that this could be her intent"...kind of gives her an out and then she can show her colors (oh my goodness you're right) or her butt (I don't care what people think)....either way you've made you're position very clear and folks can appreciate that. d

What I have found that in the long run, leopards don't change their spots. If this woman is rude and a downer, most likely you won't be able to change her. That being said, she shouldn't be allowed to alienate other volunteers or to malign those who are less fortunate.
This is a time when you have to be 'cruel to be kind'. In the long run, it will help both you and your organization. Pull her aside when you can, preface your speech with "I value you. I love you. You make a difference" and then tell her that her negativity is driving others away and you can't possibly imagine that this could be her intent.

Good luck and let us know how it goes.

I would try to push having her behind the scences. Maybe setting up, doing food, the organizing end of things. Maybe she will get the hint, but if she would ask why tell her that you feel she works better behind the scenes.
We had this issue a few years back like this and I hope your parent doesnt get as bad as ours did.

Good Luck

Tough position you are in.... but you have to talk to her-- you don't want to lose parent/teacher support because of one parents feelings.
Find out why she is so negative as events-- or maybe try and have her help only behind the scenes on things-- so she doesn't have interaction with kids/adults.