On trips, I would have my wife wear my 1-pc textile suit, and I would wear my crappy 2nd set of gear. She had her own Shoei helmet, and full gauntlet gloves. As well as a good sturdy pair of over-the-ankle leather boots.
Around town, we used to ride in jeans and textile jackets. Usually wearing hiking boots. Always gloves.
Seeing as how I don't ride on the street anymore... I don't think I would want my wife on the back unless she was wearing full leathers, and a good back protector. Motorcycle specific boots, and race gloves. If she had her own street-bike, I would expect that she would be geared up for every ride.