I think I need a bit more information. Is she moving out of the school she's currently zoned for? Will her kids still be attending this school?
If so, then I don't think you have too much to worry about. She may have plenty of help to move (churches, friends) She may be one of those people who plans ahead and is packing boxes in all of her spare time. Regardless of whether there is even a problem to worry about, I always tell new board members, (as it was told to me) your #1 duty is to find your replacement, if you were hit by a truck tomorrow, could someone come in and take over and KNOW what to do? You should always have someone who knows enough to step in because let's face it, the unexpected happens all the time.
If she's not moving out of the school, I wouldn't worry too much about it
and if she expresses that she can do the job, be prepared, but trust her that she knows what she is doing. You might just be surprised!