Do test for tick carried diseases to see if that is the issue. Might be worth doing that before doing an ultrasound and biopsy. Not only Lyme but ehrlichia and babeosis could have urinary tract impact.
http://www.marvistavet.com/html/body_babesia_infection_in_dogs.html
A bladder polyp could cause irritation and symptoms like this too.
A bladder cancer could do this too
http://www.petplace.com/article.aspx?id=67
I think I'd start with the tick carried disease testing and then go on and do an ultrasound if that was indicated. Check the bladder and surrounding tissues as well as the kidneys during the ultrasound.
Good luck with her!
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