Veterinarians will sometimes lie just to make money.
I'm not going to accuse your vet of doing this because I can't say for sure, I would be a little more skeptical though.
You said that it's obvious that your dog isn't doing well, so what makes you think that she's doing well..?

And btw if your vet or anyone says that she is suffering and needs to be put down, I just want to say this now in case I'm not here and it comes to that, please do have her put down. It's a very humane process, the dog doesn't feel pain it just thinks it's falling asleep.
Trust me it's less depressing to have them put to sleep then to watch them suffer to death.
This is something I didn't understand when I was younger and our cat had to be put to sleep. I just thought the vet was heartless, but that's not it at all.

They did take blood samples @Rouge. When we go back we will ask them what they think.

The one bit of sympathy you'll ever get from me because it's pertaining to animals and you're not gonna acknowledge it even.

):< you're a pee-face

Pee-face?

Were at an all night vet hospital she can't even walk..

We had to put her down my whole family is sad and upset

We had her for 12 years. my dad woke me up at 2 am saying she was dying she couldn't get up and walk and she had kidney problems the vet hospital said a brain tumor. I'm sad

I'm sorry about your dog.

It's okay though, your dog isn't in pain anymore.
And 12 years is a pretty long time depending on the breed, you're pretty lucky.

Her breed lasts from 14-17 years but she was 14 years old she's a cocker spaniel beagle mix and those breeds last a long time

I'm still sad and depressed but my gf makes it a little better<3