I just went through something similar to what you are experiencing. Some of you may remeber I posted about a mare rejecting a freshly clipped foal a few weeks back.
Well she acted just as yours ears back mouth open and legs kicking.
I really thought she would harm the foal. To make a very long story short it came down to me having to be VERY firm with her and persistant. First step of getting the foal back with the mom we tied her head short and held her tail for the foal to nurse. If she would kick at the foal I would kick at her(nothing to hard just to tell her it's not exceptable) We left her in stall for 3-4 days and went on like this. I would harshly tell her no when I seen teeth and again kick back if she kicked. Within a few days I could just stand there and yell no loudly and she let the foal nurse.
Second fase I put her out in a round pen where she could not see other horses, just her and baby. Again I would go in every two hours to let baby nurse.He was about 30 days old at the time. I now only had to hold her halter and give a firm no when she'd try to kick.So improvement was well under way.
Third step we let her back with the broodmares on about day 7-8, thought it was a disaster but we went out and held her every couple hours and let him nurse. We always bring them in at night so that made it easier. She was stopping with the kicking by now and was I believe relearning she was supose to care for this baby.
Finanly about day 9 we seen her briefly allow the baby to nurse alone a couple times throughout the day. We still went in and held her just to be sure he was getting enough.
Within 2 weeks everything is back to normal
It was a lot of work and you really needed to use a firm hand on these mares to show you are the boss mare and they are to submit. I'm not saying this will work for all but it did for us and I couldn't be happier
There is nothing more stressful then having this happen so I know what your going through and wish you the best. If you want to PM me about anything I'd be happy to go in more detail. Joyce