Ditto everything Charlotte says as we've done all those things here.
I've been at the barn and don't know everything you've tried, but you might try these also.
1. While the mare is tied or held by someone, have another person hold up the back leg of the mare of the side the filly is on. My vet clinic has done that with a mare and foal of mine when the foal wouldn't nurse. This gets the leg out of the way and if the foal is looking around, it puts the udder right in their face. Worked wonders here.
2. If the filly will suck a syringe, fill it full of colostrum and get on the opposite side of the mare reaching under the mare with your syringe (assuming your mare will stand) toward the foal. If the foal is at the udder area of the mare, try to get them to follow the syringe to the udder. I've had good luck doing that too. Also I coat the mare's udder with colostrum. The foal can smell it and will search for the source of the smell.
Congratulations on your filly and I bet you can get her to come around. Good luck!