Use any cheap tire. Benefit is she can train on it too, in a pinch.

I've used the same tire on the same wheel for a few years now, both inside and outside. It's a bit worn but probably good for another light summer of riding. It's a wire bead tire, I think I paid $10 for it. Schwable. But seriously, any tire will do. Your local shop may have some 650 tires they want to get rid of.

The trainer tire, as far as I'm concerned (I've ridden a friend's) is a marketing product.

cdr