I've been on this flight. The accessible lav is larger, but probably not large enough to accommodate an aisle chair, a person moving in and out of the aisle chair, and an attendant, all with the door shut (especially with some space required to stand and pull garments off and back on). IIRC, however, there are curtains that can be pulled at the back of F and the front of J, essentially creating a mini cabin for you while you are using the lav. Discuss this with the FAs at the beginning of your journey, and then again when your wife needs to use the facilities. Be polite, but firm. It is an 11 hour flight, and no passenger should be deprived of a bathroom for that length of time.