How about printing official ballots? This wouldn't have to be much; you could simply print your PTO's name and/or logo four or eight times on a sheet of paper, cut them up, and give one ballot to each person present for the election. If you don't have to be present to vote, it gets a little trickier; in that case you might need to add something that doesn't photocopy (light blue usually won't), or emboss each ballot (embossers can be purchased at most office supply stores) or print stickers that would be hard to reprint exactly and put a sticker on each ballot.

Or, depending on your bylaws, you may be able to vote by a show of hands instead of by paper ballot. It's hard to stuff a show-of-hands vote! (But watch out for people raising both hands.)

As to her family members, whether they can vote or not depends on your bylaws.

We are having an issue with one parent with PTO elections. Our board members get to select their teacher. This is a perk that one parent is taking to far. She stuffed nomination forms with her name in multiple positions and multiple hand writings. We delayed voting to determine how to handle. On election night, she brought her husband and other family members to help vote. Problem is she was PTO Pres at a feeder school and didn't fulfill the obligation. How can we handle this delicately but stop her from trying to railroad the election because she wants to pick her child's teacher.