Def check if she can get into a last minute aisle seat. If that fails, just tell her to level with the aisle seater.

I have been in similar situations. Due to a medical condition, I always take an aisle seat. But sometime the last minute upgrades doesn't allow that. In that case I've had a frank (and sometime embarrassing) conversation with the aisle person explaining that I may need to get up several times during the flight.

Over half the time, the aisle person has no problem switching with me. However, when they don't, they have told me they appreciate the heads up, and that won't mind moving for me as many times as needed. I've only encountered the d-bag aisle seater once or twice.

If she is just honest with the aisle seater, things will work out almost all of the time. The d-bag factor is always in play, but most people are very understanding.