Wouldn't recommend fighting with her at all. You want to assure her, you are not going to hurt her or the foal.
This little method works well with a lot of them. Catch the mare, put a muzzle on her. It's her mouth that usually comes after you first. Then take her to the hitching rail, let baby follow. Don't tie her, just take a few wraps of the lead around the rail, so if she has a canary she doesn't hurt anyone if she pulls back hard. Let her and foal relax. Have one person handle the mare. Try to keep her with a 2 to 3 foot loose lead. The other person approaches the foal and gets the foal to go to the mares head. Try to get mare and foal comfy with the foal at her head. Then just keep working with the foal in this location. If the mare should try and bite, you are protected. Once the mare figures out you are not going to take her baby, nor hurt her, they usually settle into letting you mess with both of them.
If you get too aggressive disciplining the mare, you may start a battle you can not win, then everyone looses.
Now the best way of doing this. And this will sound really strange. Find a young child, less then about 15 and more than 3 or 4. Old enough to listen and young enough to follow directions. Put the 3 of them in a pen, about 50 dia, or there abouts. And leave them alone. There is not 1 mare in a million that will bother a child messing with their foal. If you have never seen it, it will absolutely petrify you the first time.
First time we realized this, our first daughter came up missing. She was about 3 or 4, just walking well. Found her out in the middle of the bull field, petting this really bad tempered bull on the nose. After we clean our britches, we, as calmly as possible asked her to come in for supper. She headed toward the house and mean bull walked calmly beside her all the way to the gait.
We've had many a foal that we could not even get close too mare or foal, then find the kids out in the pasture playing with both of them.
After the kids mess with them a dozen or so times, they don't seem to mind those bigger people coming close either.