I have a 14 (almost 15) year old chihuahua. She was diagnosed with kidney failure a little over 1 yr. ago. She has been on a special diet for the entire time (KD hills). She hasn't been eating consistently for about 1 week. But has been drinking regularly and using the bathroom normally. This evening she began to vomit what little she ate and some water she drank. I plan to call her vet in the am but is there anything else I can do?

If she isn't keeping any water down try giving it to her in a syringe.
With any dog and especially one with kidney failure it's important to make sure they stay hydrated.

Just squirt a syringe full of water down her throat ever half hour or so.
If you have or can get some pedialyte it would be even better.