I suspect that your past president is terribly insecure. If things went so poorly during her term, and it's too difficult for her to take the blame, then she can make it seem like an impossible task for anyone. Then she can simply sit back and say, "See, it's a horrible job. Nobody can do it."
Also, if she was so horrible, the new officers may have been overly anxious to rid themselves of her immediately and altogether. If that happened, she probably didn't understand why and likely has her feelings hurt.
If she's still causing trouble this late in the year, she's still sore about something. The trick is to find out what it is. Ask a few questions:
What was her term really like?
Was she pushed into a "nobody else will step up" role?
Once in place, did she have the support of the rest of the board and membership?
Was she well liked and/or well respected prior to last year? But it all changed simply because she turned out to not be very presidential?
You mention jealousy, anger, negativity, being difficult. Any or all of these can be the result of hurt feelings. I'd start there.....
Some people come into our lives and quickly go. Some stay for awhile and leave footprints on our hearts. And we are never, ever the same."
"The ultimate aim of karate lies not in victory or defeat but in the true perfection of one's character."
One thing I did with a previous President was use her throughout my first year as a mentor/reference. I asked her opinion on many issues, and though I made sure that ultimately it was I who was making the decisions, but I think she felt good about the respect I showed her.
Maybe making this ex-President, as well as all ex-President, an officlal mentor to the President would be a way to make her feel better and appreciated.
If not, then the other avenue, besides trying to talk to her, would be to put her in tough spots. For example, say you are going to be discussing a topic and you have an idea that she may be negative about certain things. Make sure that you have all of the answers. Be ready to shut her down. So when she says something like "I don't think that would be allowed by central administration" (or something like that), you can come right back with "Actually I have already verified with the Central Office that this is acceptible!". A couple of these will make her back off, but your President will need to have the answers for all topics, or at least be able to quickly relay that she will get the answers.
If the discussion you have with her fails to result in immediately improved behavior, check your by-laws to see if it has a section regarding member decorum. Behavior that antagonizes other board members and undermines the overall good health of the organization is sufficient justification for making a motion to vacate that chair.
Yes, I am all for addressing the situation with a difficult person first. The only problem I see with ignoring her, is that she will continue to complain and maybe even build up momentum, therefore enhancing the problem. I think stopping her in her tracks will keep all negative behavior at bay, perhaps even holding her accountable for her actions. In the last few years I have seen an increase of problem parents who feel that they have every right to complain, bad mouth, scrutinize, etc. etc. and simply put, cannot restrain themselves to keep their negative comments at bay. I know it is uncomfortable to address the problem, easier to ignore, but neccessary to address the problem immediately. Good luck!
One of the best lines I've heard on this forum addressed this. It was the suggestion that follows lovin above. The idea was to get the person alone and say "We've noticed that some of your comments are really negative toward the group this year. I'm sure that's not the way you want to come across so why don't we discuss your thoughts/concerns so we can all move forward." or "I just wanted to make sure we all are talking in a positive way about what we want the group to do."
Just seems like a great way to keep them off the defensive. If lovin's approach doesn't work however (which is one we all use a lot) just ignore her. Everyone recognizes what is going on. So listen politely and when she's done more forward. Make her irrelevant to your group. It'll drive her nuts but that's okay.
Have you tried the "kill her with kindness" routine? She most likely has her feelings hurt after giving of her time and perhaps realizing that maybe she wasn't 100% successful. Is there a job you can give her at a function where her good skills would be used in a positive way? Sometimes just a little positive talking too can pump a person up. Try to stand in her shoes for just a minute, and maybe you will see that perhaps she wasn't President material but she can certainly be an asset to your organization because of her past experience. As for her negativity and bad mouthing, I would calmly address this to her in private as well. Ask her to vent her frustrations to the board personally, and not to other parents as this can only cause hurt feelings for everyone. Hope this helps...