Well, she's still with us!
The vet (a farm animal specialist and someone who has helped us enormously in the past with one of our other hens - he even took our lovely Bella to his own home for a whole week to monitor her last summer!) simply said Daisy's crop was 'slow', not impacted (probably causded by the original impaction, that I managed to clear myself on Sunday), and they didn't want to start pouring liquid paraffin or other stuff down into her crop when clearly she just needs to be starved for a day or so to allow it all to clear, and then given something to sort out the sourness.
He's prescribed nystatin (I didn't like to tell him that I already got one step ahead and had ordered it myself!) and it will be in tomorrow, but in the meantime, her crop feels to me like there's nothing in it but an enormous amount of liquid - I suppose that's good? She has drunk almost a pint of water since I got her home, and it's definitely going through, as her crop is getting smaller, so at least she's hydrated. Perhaps she senses that her crop needs to be flushed? I've added some Poultry Drink (special chicken supplement available here in the UK) and a little ACV for good measure.
My guess is that she will need her crop milked before I can administer the nystatin, and my other prognosis is that her crop has gone pendulous too, so she'll probably get this as a recurring issue, now that the muscles have weakened.
Hopefully she will be able to last another day or so without feed - I'm tempted to try and give her a little live yoghurt just for some sustenence and for the good bacteria, despite the vet warning me not to feed her anything!
More updates tomorrow - and thanks to everyone who has offered support, particularly jjthink and andreaS.
I love BYC!
Oh, and I love my vet too - despite having her all afternoon and massaging her and monitoring her constantly, he only charged £14.50! (That's approx $22!) How lovely is that?