I am 6'4" and my wife is 5'6". We own a XL Santana sovering and it fits us fine. There is enough room on the stoker's seat post for my wife to use a pivot plus suspension seat and to mount a saddle bag. Unless your wife has very short legs she should not have any problem.
We have not done any loaded touring but we also own a Santana Cabrio triple and the team + bike + gear is about 500 lbs. We use 48 spoke 700 wheels and can use from 28 to 32 widths. We have had zero problems with this system.