Thank for all your replies.
I gave her a dose of twin lamb drench while waiting for the vet, just in case and as I had it to hand.
Checked on her again just now, and gave her another dose of twin lamb drench.
She's still the same, lying down, legs totally floppy now, but holding head upright, looking alert, eating and drinking.
I'm concerned that in the 5 hours she's been in the shed she's only pooped once (just now, after I gave her the second glucose drench.) I found at least one source saying low volume of dung and gut reaction after glucose dosing is a sure sign of ketosis...
Not sure if she is developing a bloat or not - she looks a bit wide the way she is lying down, but that could be just me. There are clearly noises in her rumen, and what seems to me regular regurgitating 'impulses' though her body, but no cudding, at least not while I'm watching. Or could it be that she won't cud while I'm in there with her (trying to observe her calmly for some time each time I visit, after dosing etc.)
Should I give her a bicarb/oil/yoghurt drench as well?
I don't have combivit here but I could give her a jab of intravit (vit B12 only)?