Agreed...tie or stall the mare, and focus on the gelding. I highly doubt the mare is 'afraid' of you as well, she is probably just frisky because it's chilly, and wants to go for a good romp around the pasture. I've ridden in pastures with other horses, and sometimes just having a person on one of the herdmates gives them extra eagerness to play, not sure why, just does. So tie her up, or put a saddle on, and make that gelding work his tail off when ever he gets prancy; just because there is another distraction there, doesn't mean he shouldn't have to respond to you.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."