Thanks to everyone who posted. Just wanted to report back to let everyone know that with hairball-control food and a few doses of KittyMalt (which she hates), Boo is doing much better. Haven't found a single pile yet (knocking on wood).
It's nice to know there's a community of nice pet-owners like this to help out and dispense advice to silly people like me, who mistake hairballs for poo!

Kim