In that case she takes her vote-by-mail ballot to a polling place, surrenders it and then votes. Not a complicated process.
Read the article. It’s most interesting. If the situation continues, the Republicans will never win another national election. My situation will be okay no matter who wins, because I have a federal pension. I am as helpless as the rest of you in stopping the juggernaut that is our national debt. Our kids and grandkids will be the losers. But as the nation goes irretrievably downhill, I figure I can at least keep my head above water. I’d like to see more drilling for gas and oil, but if it’s not to be, what can I as a helpless citizen do about it?