If the cat is peeing that much at once I'll buy you lunch if she isn't diabetic. How old is she? Has the vet done any blood tests lately?
Our now 13.5 Y/O cat developed diabetes about 2 years ago. With cats you don't really notice how much they are drinking but if they are peeing a lot, it is a problem. The smallest cat (~8 Y/O now) pees a ball smaller than a golf ball. The younger cat digs to China then pees as much on the bottom of the box as in the litter then covers it. PITA as it kind of glues the litter to the plastic. The diabetic cat was making a huge amount of wet litter. She would cover it but it was more like a spill than a localized "deposit".
I second the diabetes thing and having her tested. I actually hadn't even thought diabetes, I was thinking UTI or something, but diabetes is a great point too, UTI was just the only issue i knew of at the time.
Also if it is a health issue, don't waste money on hills science diet or any of the prescription stuff, i could direct you to a very good food that's still a hit pricey but much cheaper than that stuff