problem horse

["guest@endurance.net" <guest@endurance.net>]

patti gene@dreamsoft.com
I have a four year old mare.She has been doing very well on the trail, I usually go out with one to five people. When I go out alone she is really good, she walks out great and will go just about anywhere for me. When I go out with one she likes to lead but i she is in back its ok.When you add more riders and put her in bck that is where my problem starts. She jiggs, for hours,she YANKS her head from me continously, if i put pressure on her face she picks her head up I get the slack out of the reins and then she yanks her head down, when we go down hill she does it, I thought it was a problem with her saddle because when she started doing this it was going down hills only, but when I rode her alone she didn't do it. It really gets tiring. I am sick of this and have been told to use a tie down, she yanks her head down I don't want to ride with anything that she could get her foot hooked through. I would like to learn how to get rid of this habbit and not just make it hard for her do. I need to learn  training techniques. I have tried side passing to try to get her mind off of getting caught up with who she wants to be with but it isn't working. If her nose is stuck up another horses butt she won't jig but I won't let her ride like that, I wanted her to go out on the trail by herself because we would always ride with big groups (she did fine then) but was afraid to go by herself. anyways all you horse people  HELP!!!!!please.