Yes they can get cystitis, the most common sign is blood in the urine, but also frequently trying to pass small quantities of urine.
You can give dogs cranberry juice, or cranberry tablets, but I would be more inclinced to take her to the vet first for a urine sample test as prolonged use of cranberry juice/tablets can cause some types of bladder stones.
To get a urine sample, wait for the bitch to stoop down and slide an old baking tray or something similar underneath her, the vet only needs a small amount to confirm diagnosis.