Cockatiel with soft chirp. Possibly sick (?)

[Zukarin]

I’ve been worried about my cockatiel for a little while now. She was doing this growl sort of thing for a couple weeks, but I think that was my fault for giving mixed messages on if it get her what she wants or not. Tuesday, though, I did spent a few hours in a different room, and, when I found her, her chirp was off, she had polyuria, she was weak, it looked like she may have issues with breathing, and it looked like her wings were possibly drooping. I put her in some heat and she got better.
The next day, we took her to a vet. The vet said the same thing as a week before: she was just scared of me and being defensive(she was climbing towards me though, why would be scared of me and walking towards me??) I could have possibly agreed with the vet if Hebe didn’t have polyuria, weight loss, and weakness, but the vet ignored that when I brought it up. (I’m never going to that vet again) The vet said she’d take an X-ray or study the poop in the cage, but the X-ray machine was broken and there wasn’t enough poop.
Today, she’s just acting mild-mannered and soft-spoken. Her crest is usually up, and she pecked at me for the first time in weeks. She’s like a different bird suddenly. When she chirps, it sounds much softer than before, and it worried me.
Could it be behavior, or is there something that needs to be seen by a new vet?
(Ordinarily, I would want to take her straight to the vet, but my mom, who pays, has already paid $60 in vet bills for Hebe alone among all the animals we have)

 

[Laurasea]

I'm so sorry you are going through this.
I'd say trust your gut. Weight loss wing drooping trouble breathing and watery poop abd seemingly week. I would seek a new veterinarian, for a second opinion for sure.