The following list may be able to help with some financial aid. I haven't checked the links lately so there may be some inactive links.
Having Trouble Affording Veterinary Care? : The Humane Society of the United States
AFRP Financial Assistance for Pets
Saving More Lives Together : Asheville Humane Society
ANIMAL ASSISTANCE LEAGUE OF ORANGE COUNTY
FAQ | ASPCA
Speaking for Spot: Dog Health Care Tips & Veterinary Advice | Financial Assistance for Veterinary Care
Find financial assistance with veterinary care | RedRover
Vet Bills: Organizations Offering Financial Help | Truth4Dogs
Did the vet(s) ever do a culture or was it just a urinalysis? A culture from a sterile sample is the method that should be used to determine which antibiotic will clear the bacteria in a UTI. Judging by your post, they were just throwing antibiotics at her and hoping? Sometimes it can take more then 2 weeks to clear up. Next question is did they just do xrays or was an ultrasound done? It took doing an ultrasound before the stone was found in my lab.
Check the label on the yogurt you are giving your dog. It should be plain yogurt with live culture. Double check it doesn't have any of the fake sweeteners in it (some of them can be deadly to a dog).