What stage kidney disease would these results reflect

[cathyus_susie]

My vet prescribed SMZ's for my dog Susie for a leg sore and said to continue until the leg was healed.  Three weeks later the sore was somewhat better but not by any means healed, but Susie began not drinking much water and she wasn't hungry.  Another trip to the vet revealed kidney disease and possibly liver issues per the vet.  The lab work is as follows:
BUN 37, Creatinine 2.1, IDEXX 17, Sodium 140, Potassium 6.1, Chloride 106, Albumin 2.6, ALT 132, ALP 291, Lipase 964.

Can you tell me what stage kidney disease this would be please?  The lab work was as of 6-2-16.  I've searched the internet but couldn't find any info that says SMZ's may cause kidney problems, but I suspect that to be the case.  Do you have any idea?

When I asked about the severity of kidney problems she said it was early to mid stage and gave me ProPlan NF dry dog food and suggested I start mixing it with the other food Blue Senior) to transition.  Susie didn't find it very tasty so I mixed chicken broth in with a little bit of boiled chicken and carrots.  The vet said this would be ok.

I've had Susie almost 16 years and she was probably about 1 year old when someone dropped her off in my neighborhood; I was lucky enough to find her.  She's part lab mix, and the best girl anyone could ever have.  She's 51 pounds and has arthritis issues in her hips, her hearing is going and so is her eyesight.  Last weekend she had trouble getting up and the vet gave her a shot of Dexamethasone and Prednisone 10mg tablets 2x per day etc.  She became weak and her back legs were unstable after a day of medicine.

How does all this impact the kidney's?  She has diarrhea from the Prednisone and now doesn't want to eat.  My poor girl, I don't know what to do.  Do you have any suggestions?  (I reduced the medicine to 5mg a day and have now stopped it, as I read it couldn't be stopped immediately and have started giving her yogart to help the tummy. the vet says this is the kidney disease.   I'm thinking I may have to put my baby to sleep and am beside myself.
Any suggestions?

Thank you
Susie's mom