I get up a lot during a flight as well and that is why I always chose an aisle seat. Your wife should go to the gate as soon as the flight is opened and ask the agent to let her know if an aisle seat happens to open up.

If she is stuck in a window, I wouldn't worry about getting up if I was her. If she in first at least she is only disturbing one passenger. She should also see if a window bulkhead is available. A lot of aircrafts have enough space you can crawl over the person in the aisle seat without them getting up.