I am sorry that it's turned out to be her heart. You obviously have a great and very open vet which is magic and will hopefully help a lot.
It took us a couple of weeks of treatment to see a difference on the furosemide, I did the same thing as you and worried when I didn't see a difference straight away but it does take time. Oidhche was on Enalapril as well and then Pimobendan (Vetmedin) after consult with the D!ck vet.
If you end up trying the Vetmedin I have some here I could send you from Oidhche, I don't think we even used any out of this bottle. It's in date until September. It cost us about £40 so would save you some pennies? I would have to be a cheeky cow and ask for postage though as I have absolutely no money at all (a friend has been bringing me food) and couldn't actually send it to you otherwise.
I'm really sorry to sound so stingy if I had the money I would just post it.