Your dog needs to go IMMEDIATLY to the vet! This is a serious problem!!!
I work in a vets office and I have seen dog's die from this in a matter of hours. You are lucky that she is still ok.
Please take her to the vet.
Good luck
she was two years old in nov.07'and she was spayed in may of 06'.she does not seem to have any pain when she pees or trouble peeing.
How long ago was she spayed? Has it been several years or was it recently?
If she has had urinary tract infections before, there is a high chance she could have one again. Urinary infections can pop up very quickly and be cause from the tiniest things, just like in humans. She could even have smalls tones in her bladder as well that are being passed.
Watch when she piddles next time and see if she has any distress or pain, or if you see her going several times in a row with very little comming out.
She may need to be put on a specific diet to keep her from getting these infections.