If it were ME looking for a solo RV, it would for sure be a class B. A fully self contained van with a couch/bed would do me just fine. I traveled/camped out of a regular low roof van with a bed and a porta potti for years before wife/kids. But it's not me, and it's hard to say what your 63 year old Niece will want!
As to length, I can tell you that 30 feet is too long! I mean it works fine and we can do what we want, but I'm not taking it downtown for sightseeing. I can't use a normal parking lot without taking up at least 2 spaces, and need to pre-plan things more. For solo travel, I would not personally want 8' of width, or any more than ~22' long.
