The problem with a UTI is that once you have one it's not really just going to go away. Using extracts to create more acidic urine and hydrating will help alleviate some of the discomfort but chances of that ending a UTI are very slim. They're get as maintanence measures but not to actually get rid of one, especially if the dog is elderly as they prob have a decreased immune system to begin with.
I would really caution away from home treatment. If you call the vet an explain what's going on and that you can't afford an exam they may be willing to work with you or point you in the right direction for someone who can. It's at least worth a phone call or two.
Seconding D-mannose until you can get her in to a vet, which SHOULD happen ASAP. I've seen D-mannose actually cure UTIs in people (confirmed with urine cultures, it was recommended by a urologist for a client who had an antibiotic resistant strain of bacteria) but make sure she gets in to a vet to be sure.
D-mannose does not work by making the urine more acidic. It is a sugar that cannot be absorbed by human cells (or dog apparently). It was originally concentrated for the use of diabetics so they could get the benefits of cranberry too.
You ingest it. It's absorbed into the bloodstream though the upper part of the digestive tract. There it circulates through your blood, not being used by your cells, until it ends up in your kidneys.
Once it hits your kidneys the D-mannose sugar molecules bind to individual bacteria and virus pathogens and carries them out of the body when you urinate.
So it does take a full on regimen of taking it a couple of times daily for a week or two at least to clean out a UTI using the stuff. It's good because the bacteria or whatever doesn't build up a resistance to it, and it doesn't disrupt your gut flora.
It's more expensive than antibiotics though. One bottle of loose powder is around $45. It takes 3 bottles to treat an adult human for one month.