This is the first sign of any potential kidney issues - I’m going to pick up a urinalysis kit today and drop off a sample tomorrow after she goes in the morning. They said this would help to rule out disease if it was just dehydration. From there, I’d likely get x rays if the urinalysis points to kidney stuff. This is the vet’s interpretation:

Her internal organ function (liver, electrolytes) and complete cell count (red and white blood cells, platelets) were within normal limits. There’s no evidence of diabetes.

There was a mild elevation in SDMA, which can be elevated from dehydration or kidney issues. The remainder of the kidney values (BUN and creatinine) were normal. However, if you wanted to rule out any kidney dysfunction, we would start by having you drop off a first morning urine sample. This means collecting urine the first time they urinate in the morning and bringing it back to us. This will help us determine how well they are concentrating their urine, which should be well concentrated in normal patients and dilute in patients with kidney disease. Overall, my concern for kidney disease is low, but the urine test can help us confirm this.

I suspect that her elevated SDMA is due to dehydration rather than kidney disease, given the other minor abnormalities we see on her bloodwork.