I applaud you for wanting to make things better. Unfortunately, I'm not sure there's a good solution or a way through this that won't turn ugly — and still probably won't achieve the result you hope for.
You can go to the meeting armed with a copy of Robert's Rules and challenge the way the election is being held. You can try to rally support by bringing other parents to the meeting who agree with your point of view. You can talk privately with the principal to express your concerns about fairness. (You would have to present a reasoned argument without emotion to have any chance of making a dent.) Once you've done that, there isn't really anywhere else you can appeal to.
Sorry I don't have more to suggest. Good luck, and please let us know how it goes.
Our principal and co-president are violating our bylaws to get a certain person elected to the open co-president position. They used the bylaws to get the word out (in the school newsletter) that there was an open position. The co-president, principal, and treasurer are trying to get the current co-president out and want to ensure that their canidate wins by not notifying the membership of the slate of nominees. Our bylaws state that the membership is to be notified of the slate 15 days before an election. That was not done. I brought this to their attention, and the principal buried the slate on the PTO page that few people even know exist (even active volunteers don't know it exists). To be fair and in the spirit of the bylaws it needs to be notified in a way that would reach a majority of the membership like the school newsletter. When I mentioned that I was told to stay out of the matter. I am one of three nominees. The current co-prez, myself, and the favorite. This is not a matter of whether I win or lose, it is a matter of holding fair elections. This board has violated election and many other bylaws. Our PTO is no longer a membership organization. There are no discussions in the meetings, and a vast majority of issues are never brought to the membership for discussion. The executive board makes the decision and informs the membership of what it will do (even if the decision violates the bylaws). I am seen as a threat because I am challanging the status quo and I am not a "yes man". What can be done when the principal is part of the problem?