Dogs sometimes get urinary tract infections or stones.
If you find your dog constantly waiting at the door to go outside to urinate or if you find blood in the urine please be cautious as there may be a urinary infection or the presence of bladder crystals or stones.
If you let your pet outside and you catch her straining to pee, squatting but not passing urine or her pee is very little, then you know something is up.
Try to give your pet lots of water as this may help flush out her system, but it will not fix the infection. It is a good idea to pay a visit to your vet. You may be asked to bring in a urine sample which with a male dog is easy but with a female you could try to obtain by collecting a sample mid-stream in a plastic container as the dog eliminates herself.
Your vet may suggest x-rays to be able to see if there are crystals or stones. Your veterinarian may put your dog on medication to dissolve the crystals or prescribe other treatments.