It is??? I thought the main reason for 650B was in converting a 700C road bike to fat tires while still being able to fiddle brakes to work. Otherwise, 559 (regular 26") wheels will be shorter still, and have many times more tire choices. The bike pictured has discs, so she's not limited to any particular size. 650B are just the fad-of-the-year because they're halfway between 559 and 622.

I'd just get a whole new bike, but that's just me.