I have just replied to your other post, but having seen this one, I will add that I wouldn't think that joint supplements and herbs will be much use to a horse so lame/in such pain that you describe her as hardly being able to walk.
Is your vet a specialist equine vet? Has your horse been x-rayed or scanned at all? Was the diagnosis made at the yard, or did she go to the vet hospital?
we know she has already got a tewisted pelvis she had that before we got her the vet recons she has not it and moved it a little out of place she said it is pointless in x-rays with her backend being all over the palce any way. Yes it is an equine hospital. and we know it is muscle spasm because we have had the ostepath out!