Why wont my horse join up?

I tried joining up with my mare today and it just didn't work. I sent her cantering around the round pen, eyes locked on hers, shoulders square. I sent her both to the left and to the right, looking for all the signs of join up (one ear locked on me, licking and chewing, head low to the ground) but she didn't do any of it. She just totally disregarded my actions. After a REALLY long time of her doing mindless circles, I gave up. Is she testing me? Is she doing this because she's been the alpha mare her whole life in the pasture? Please help! I really want to bond with her but I feel like there's a wall between us!