Dear Luna. She sounds a character!
I think it's a good idea to find out what the vet thinks it is as that will help with treatment option decisions.
I've had quite a few hamsters spayed. My vets now expect my Syrians to make it through the surgery which is different to when I had my first girl spayed 10 years ago. Chinese hamsters are a bit more touch-and-go.
21 months old is tricky as it is older than I've had most of my Syrians spayed, but she may be older or younger than that. I'd suggest having an open discussion with your vet - it will depend on her body condition now she's had some antibiotics and also your vet's experience and comfort with spaying small animals. Even if the vet thinks it's a pyometra, you would need to be prepared that sometimes they find things aren't what they initially thought when they do the surgery.
There are other options if they think it's a pyometra. I wrote about them
here.
I currently have a 2 year old Chinese who has bleeding too, and is also on baytril and painkillers.
Good luck to you and Luna.