I’m sorry, @4horses. Not being entirely confident in your vet doesn’t help your stress level at all in a situation like that. If it makes you feel any better, a friend of mine had a maiden mare foal last week after dripping milk for almost two weeks. She was able to find frozen colostrum locally to give the foal, but he still ended up with an IgG under 400 and had to receive plasma.
I would probably go ahead and order milk replacer in your situation. I tend to err on the cautious side. Hopefully the treatment will bring her milk in, but, if not, at least you’ll be prepared.