OP, I think this is definitely one for the vet. It's likely the teeth are causing the problem but that's not definite. Both the twitching, and the extremely late eruption of potentially wolf teeth would both have my asking my vet for advice.
I've never heard of a situation like that! It might the teeth causing pain or it also might be a bad habit that she has(?) And maybe the eye and ear twitching is just natural for her, she can't help it. All of these are ideas and I'm not a vet so you should talk to your vet about it!
I don't know if I'm correct, but what if both problems are connected?!
What if the wolf teeth were growing inside and it was painful to her and that's why she got all twitchy when having the bit on or something connected to that!
So a mare at my barn, Torrie, is an OTTB. She is 14 years but has had this problem for many years. We can’t seem to figure out what is causing it...
Some of her medical problems: TMJ and kissing spine
When the bridle is on, the left ear and left eye twitch. She pulls the bit out to the left side of her mouth so there is “extra” bit on the left but not enough on the right. This is NOT rider error! I know people might say it is but when ridden with no rein at all she does this AND she does it when nobody is even on her yet. Another weird thing that may contribute to this, although I’m not sure, is that she just started to get wolf teeth. This is also a mystery... only about 20% of mares get wolf teeth/canines, and when they do get them it’s around the age of 4 or 5, but Torrie’s just came out this week. Any answers to that also?
If anyone has any idea of what it is or how to treat it that would be wonderful! Thank you so much!