My suggestion would be to make sure it wasn't against your by laws and make a decision as a board if it is NOT. We as a board decided to tap into the Kindergarten parents to try to get some new excited blood on our board, to help us boost parent involvement for next year. We have filled one of our committee chairs w/an incoming K mom. We had one position that another incoming mom wanted but another mom whose child had attened Kindergarten this year, who was a great volunteer also wanted the position, so we are giving her the position. I guess what I'm saying is to go w/what you feel is right. If you struggle to get the parent invlovement you need (like us)personally I think it's a great idea.
It sounds to me that this parent isn't eligible to be a member until her child starts school. Assuming your elections are held this spring, she's not eligible. If the position is still vacant in the fall, she could be appointed to fill the vacancy.
Our bylaws allow incoming 2nd grade parents to vote in our spring elections, because they are coming from our K-1 feeder school/PTO. We would also allow them to be nominated for office, but that's specified in our bylaws. If a parent were moving in from another district, they would not fit that criteria and would not be considered a member until their child started at our school.
I believe our bylaws require a minimum number of meetings to be attended before someone can be nominated for a position. Is it possible you have something like this to help you out with your question?
The irony of commitment is that it’s deeply liberating-in work, in play, in love. The act frees you from the tyranny of your internal critic, from the fear that likes to dress itself up and parade around as rational hesitation. To commit is to remove your head as the barrier to your life. --Anne Morris