We went to PetSmart last night and looked at what all they had. They had a scent-releasing collar (which is what I prefer), but it was $120!
The display also had a sonic collar, which I was very interested in, but they were out of stock.
The sales lady recommended this pheromone thing -- it's like a Glade Plug-In -- that releases pheromones that are supposed to be something her mom has naturally, so it's supposed to calm her to prevent her from barking. We're going to try that, in combination with shutting her in our bedroom, for a few days.