I would give the filly a chance to nurse on her own and see how things go.... sometimes too much interferance too soon can be detrimental. I would have your vet out to see about your mare and see if they think she has enough milk, and sometimes it comes in on it's own after the foal is born and nursing.
Some friends had an unusual case this year though, the mare foaled a bit early- a healthy colt, but she had next to no milk. The foal failed the IGG test. During his transfusion, his heart quit- the vet had to inject medication to his heart to bring him back- a bit unnerving for the owners and the vet!! All the drugs in the world did not bring that mares milk in... she has some but very little. She mothers the colt and he nurses, but they have been bottle feeding him also since birth and he lets you know when he is hungry! He is doing great, but mama just didnt have enough milk.
I highly recommend your vet come out if you think there is a problem, and if it doesnt get enough colostrum, time is of the essence. (Havent read all the posts, so you may have called your vet already)
Hope all works out and the mama and baby do well.
Just edited to note- I see you already got them to the vets, and congrats on your cute baby!