Thank you all so very much.

I have spoken to the vet about Daisy's test results and it seems very possible that she had a fast growing tumour in the lung. They can't say that with 100% accuracy because that test was not run when she first became ill, but the problem was definitely not with her heart, or asthma as a couple of people had suggested.

If it was an infection, then the antibiotic had not made any difference, she was getting worse. The first night we took Daisy to the vet, she said that the fact that her chest had been clear two weeks previously pointed to something other than an infection. That surprised me, but she said that cats will normally fight an infection for longer than that before it becomes a problem.

All in all, I think the concensus of the three vets that she saw, and the test results, point to a tumour.

Samantha and Jessica have been out-of-sorts, but they seem a little better today. So far as I can tell, they are not looking for Daisy though. Hopefully they understand.