The response I've had from vet is they don't want to enthusiase as shes so young.
Clearly not a farm vet.
. Most commercial lambs head off to the abattoir at 4 months or not long after.
Things don't add up from your description and what others have said. I think you must try harder to get hold of a proper farm vet. If you've identified a practise that serves your local farms, I would suggest going to the surgery and talking to the receptionist, rather than leaving a message. Or at the very least saying in the message that you fully appreciate that this is going to be expensive and are prepared for that, but you have an animal that is suffering and you need to do something. You may also need your current vet's blessing; no vet will knowingly 'poach' a customer but will be happy to be a second opinion with the original vet's knowledge.
In my experience, most farm vets are delighted to be asked to help an individual farm animal, but will say if they think it's not likely to work, not the best option for the animal, etc. It may be that I've just been very lucky with my vets, I suppose.
Best of luck, do let us know how you get on.