Thank you everyone for all your input. In the end, the farrier had an attack of guilty conscience and turned up early yesterday just as I was ringing another farrier, and whipped the shoes off (using Roux's 'cracking' method) in a trice. He won't be coming back here. The good news is that the nail came out clean - no pus - and in fact she is much less lame than on Friday. I don't know if this is thanks to the antiinflamatories I've given her over the weekend. The whole nail episode is a bit of a mystery to me, as Patty commented. The nail was awful, but I too would have expected it to cause problems straight away, not a sudden flare-up after 3 weeks, and an equally sudden absence of the acute symptoms even before the shoe was pulled.
Anyway, it sure was a blessing in disguise, because it jolted me into getting those shoes off.
Smrobs, you say that with those feet how come she isn't lame. The thing is, she IS lame, independently of the nail, and has been on and off for some time.That's why the vet came to do xrays. I had her barefoot over the summer and was trimming her myself in the absence of any barefoot trimmers. I've backed up her toes and her heels have opened a little. I'll do some photos today and look forward to some advice, as I'm not too sure what to do with her heels. I recently read one of Patty's posts about bevelling the front part of the hoof to help breakover , which will surely help her a lot, as she's a toe-firster. ("Not surprising with those feet", I hear you all say!).
Still waiting for the xrays so I know for sure what's going on in there. I put my bets on navicular pain, though the vet wasn't convinced by the idea. Said her heels didn't look bad...??
The shoes now provide an interesting comparison of her hoof shape - see photo. The sounder hoof measures 3cm between the heels whereas the shoe off the lame foot only measures 2.3cm. You can see the difference in the photo of her forelegs too.
I'll be back later with more pics. Thanks again all for the Great input.