Ignore her and conduct your PTO business above board and it should work itself out. Sure their may be some long meetings (if she attends) due to her questions, but after she sees that all the finances are accounted for and your board is doing their jobs correctly, she'll stop.
Make sure that you have a monthly statement at every monthly meeting and the income & expenses explained. That will show that you are not hiding any information from anyone.
As far as her not liking people on the board, well, she just has to get over it and grow up. Parents will get tired of her negative comments and begin to brush her off; especially when you prove that you have good intentions & there is nothing to be concerned about.
A couple of our meetings actually got a bit "personal" with comments about parents and teachers. This year, we added an excerpt directly from our bylaws onto the top of our meeting agenda. It's actually kept the meetings very positive.

The public meetings are reserved for reading the minutes, budget information, old business, new business and current updates. Criticism of individual teachers, administrators or parents shall not be voiced in open meetings or executive sessions. Any individual problems arising shall be taken up outside the public meeting. Discussions regarding the above mentioned shall be addressed with either the President of the PTO or the Principal of the _______ School, in accordance with __________ School's policy.

I'd take CCs approach and ignore it. If you'd like to put something out to the PTO at large reference your finances and invite everyone to understand the procedures you have in place, the safeguards and processes...then do that as information for them. Not to answer her allegations but just as a preemptive strike..make it a part of a "Know your PTO" series in your newsletter..actually I like that and may start one myself...

d

where does all your info come from? direct from the source or from the rumor mill (every school has one).
if its not from the source, dont trust it one bit.
talk directly to the person, in an adult manner and in private, have a coffee together or whatever, clear the air and make sure ALL the hearsay you have heard is the truth (it rarely is).
good luck. it doesnt sound like a problem at all, beucase if in fact the rumors are true,that person loses all credibility (unless her suspicions are based on fact) and no one will listen. dont give her the attention she seems to want, AFTER you have determined if its all baseless silliness, all that youve listed here.

There is no part of the body which varies so much as the human ear. Sherlock Holmes

Have you asked this person where she got her information about the "stealing" of money? If she is so concerned about the group's integrity has she shown up at meetings and voiced her concerns or she just gossiping about?

I would start by speaking with her face to face and sincerely ask her what information she has in regards to the stealing and why she feels the need to be so negative about your group. Speaking with her should at least give you and idea as whether there is any merit to her "concerns". Then I would expalin to her how negative comments made outside of meetings can give people a bad impression of the group because there may be parents who don't know what is true and what isn't. Ask her what her thoughts are as to what the PTO should be doing for the school and if she would be willing to become a more positive voice for improvements. Just talking to her may be enough to get her to stop.

I am curious, why does she think people are "stealing" from the PTO? Is the budget shown to the members, along with the account information, so that there isn't any question in regards to how the money is being used and why the balance is what it is? Has there been any problems such as the PTO suddenly not being able to fund a planned event or events? Anything that would cause questions about the finances? Does the treasurer go over the account at each meeting? Is she at the meetings?

What doesn't she like about how things are being done in the PTO? Is it an open group? Are notices sent home in good time for the events the PTO puts on? Are there opportunities for her to help out and put her energy in a more positive approach? Are meetings open? Is there ample notice of when the meetings will be held?

Has this member volunteered for any of the programs? Does she do any other type of volunteer work at the school? Is she active with her kids classes?

I guess I am just simply trying to get the full picture here....

But like Crewchief said, if she is out just to make trouble and not interested in actually doing work for the PTO, school, or classes, then simply do what you know the PTO needs you to do ~ focus on the programs and such for the kids, not her. "kill her with kindness" I guess is the best approach and if she is out to just bother you, when she sees she isn't then she might just fade away! Good luck!

Do nothing at all with her. She will spin herself into the ground with our without your help. Surely everyone around her knows what she's up to. Those who don't soon will.

It's confusing to me why anyone would purposely cause trouble "just for the fun of it" but sadly those types of people do exist. The more you try to deal with her, the more fun it gets for her.

If you cross paths, be pleasant. If she tries to draw you in, resist. Keep your head high, continue to do the good work you're doing and your reputation will speak for itself.