Hi,
This sounds like a difficult situation for you to me stuck in and I am not sure any of my advise will help greatly. I would suggest trying to call all the vets in your area (look them up on the net or in the phone book) and explain the situation, your dogs symptoms and ask if they may be able to help you with a payment plan. Do you have any rescue-type organisations over there that could help with treatment or a donation? In the UK we have the RSPCA and Blue Cross that sometimes help owners with limited funds.
You could try worming your dog, you can usually get a worming tablet from a local pet store or over the counter at a vets - it sounds like she has fairly serious problems but this might help in the short term. You could try feeding very bland food (boiled chicken/white fish and rice) instead of normal dog food for a while to see if this helps stop the running faeces. You could slao feed little meals more often than usual to allow the gut more time to digest smaller amounts of food (makes its job easier). Drinking lots and weight loss could also be symptoms of something like diabetes and usually these dogs eat alot too. Was she overweight at all? Diabetes is common in middle aged, large breed, overweight female dogs.
I would try and get to a vets if you can. Hope this helps a little.
Good luck, Jo