9 year old doxie with symptoms of Cushing’s with normal test results

My 9 year old mini doxie has had some symptoms of Cushing’s disease since March or so. She’s been exhibiting the following:
- Excessive thirst
- Going outside to pee multiple times in an hour and urinating large amounts at a time
- Hunger (although this one is hard because she’s always lived to eat and has been food obsessed)
- 1lb weight loss since March with no food or activity changes
- Sleeping more
- Some minor hair loss on her tail
- 2 episodes of urinary incontinence in her sleep and more accidents at the door if I don’t get there quick enough

I have taken in 2 urine samples from two different months in to be tested for UTI and they have been negative. They said her urine is also very diluted which makes sense for how much she’s drinking.

Last week I took her to the vet and we decided to start with normal blood work. All her blood work, including liver function, kidney function, glucose were all normal. I was honestly shocked. I thought it would be a slam dunk. My vet is suggesting we do the 8 hour fast - steroid testing for Cushing’s disease. I’m not against it, but why would all her other stuff be normal then? We’ve spent so much money the last 2 weeks on both our dogs so cost is definitely a factor.

Did anyone else have a dog that had normal blood work but failed the dexamethasone 8 hour testing? I’m trying to decide what to do.