Maggie has had many bladder infections. I tried the cranberry juice trick, but not sure if it really worked. Actually, it took a continuous treatment of antibiotics to kick it out of her system. She had these infections before and after she was fixed, so don't count on it being a cure all. Also, my Aunt recently told me that food with a lot of ash in it can cause problems.
I have a great trick for collecting urine samples. I keep Maggie on the leash (close enough to me) and as soon as she squats, I slip a lid from one of those disposable plastic containers under her. I put the lid upside down so that the urine doesn't spill off. Then I pour it into a baggie. Keep in mind that some of the urine may touch your hand , but this trick has worked for me every time. Good Luck!