What is the rest of her diet like? How much turnout and stall time does she get? Both diet and turnout play a HUGE role in horse behavior.
I would evaluate the above and make changes if possible before starting her on supplements. After you make some changes (give it 20-30 days to see the results) and you still want her calmer, you can consider different supplements.
A friend's mare is the same way about her face. It makes deworming interesting... We have been using clicker training to get her to WANT her nose to be touched. It seems to be working