Hmmm...I've never heard of people with gallstone problems having pain while peeing. (anyone else know more?) Give her some 100% pure cranberry juice (expensive, yes, but it can't be Crancocktail) and see if that helps - if she has an infection, it will clear it.
Maybe she has Kidney Stones?? In that case she has to drink gallons and gallons of pure water to push the stone out...Get her drinking tons of water right now no matter what...