If you take her to the vet, try to take a urine sample with you. Sounds weird, but we let our dog out in the morning(when she has to go bad) and stick a soup ladle under her when shes peeing. She has to go so bad she doesn't care what your doing, and it saves her from having to have the vet inject her to get a sample. Just make sure the ladle and bottle are very clean so the sample is not contaminated.
I'm no vet but it sounds to me like it could be some sort of kidney or bladder problem if the smell is strong. I'd call the vet to see what they say. If they say come in, get her there. It might be something simple to fix. Best of luck. Hope this helps. :)