My experience with pet kidney disease was with my cat, KC and unfortunately, the disease is deadly.
One thing the vet told me was to change the diet. KC was to stop eating dry cat food, and instead eat the moist can food kind. The vet should provide you with the proper pet food for your dog. But be forewarned, it is not cheap. I bought a case for KC and she only survived long enough to eat 2 cans. Thank goodness I could get a refund for the unused cans.
Since you are in the early stage, try the food. As the kidney disease progresses the vet could prescribe a water treatment for your pet. It is like dialysis for pets. But again, it is not cheap.
The sad thing is, is that there really isn't a lot that can be done and in the end can be very expensive. I know how hard this is and will be for your mom and your family. KC was diagnosed and with in 2 weeks she was gone. I had to put her to sleep because she refused to eat and drink and wasn't doing well. Watch the dog and make sure he/she is still eating and drinking. He/she will probably sleep a lot as the disease progresses. If he/she eats and then vomits what was eaten, the dog may not eat anymore and then it is down hill from there.
Please note that this was just my experience and I hope that your mom's dog will be different and not as heart wrenching. Your mom's dog may totally handle kidney disease in a totally different way.
My thoughts and prayers are with you because you have a lot to deal with and will have a lot more to deal with. Pixie dust and happy thoughts are being sent your way.