Re: Do you know why she might be doing this?
Chelle, the cost of the litter isn't of any importance to a cat. Cats have different preferences for litter. In addition to adding another litter box, you also might want to try a different litter. Switch to a different texture, or non-clumping if you're using clumping, non-scented if you're using scented, etc. Just try something different for several days and see if it makes a difference.