Cranberry juice will not cure an infection if it is already there. Cranberry juice helps protect against infection before it happens. But if the infection is already in the urinary tract, the best thing to do is to keep the dog well hydrated, and get them to a vet as soon as possible before the infection can spread upward to the kidneys, causing serious problems.
Bladder infection are uncomfortable for pets like they are for people. But can easily be treated with antibiotics.
A bladder infection doesn't really require a trip to the Emergency vet, but it's better the dog should go to the vet first thing in the morning. The best thing to do for your dog right now is to provide lots of fresh clean water.
To help prevent another infection in the future it is best to keep her clean, and have her spayed.