I'll bet she's coming in season too. Cav's mare used to do that to Tennessee when we were trail riding and she was in season. She'd just STOP and wouldn't budge. We finally had to stop letting her go first when she was like that. It was kinda funny coz Tennessee'd just stand there like "And what do you expect ME to do about it?!"
It's true... Both mares are in season. Poor gals :~D
Sarah Lee can act real slutty at times. The thought has crossed my mind of a gelding trying to mount her while I'm in the saddle so I tend to over-react and run off friendly horses if they come close.