If the horse is really new to you, it might be one of several things. First, she just might not be as sweet as you think if the previous owners had planned your visit so that she was tired, just got fed, and was happy when you visited. But even if she is a perfect horse for them, there might be some new things going on, especially if she's fussy under saddle at transitions like from a trot to a lope. If she's a weekend warrior, at this time of year she just might be out of shape and working all those muscles makes her tired and sore. If that's it, just warming her up, getting her in shape, and taking it a little easy until she's nice and conditioned will help. The thing she does with biting your leg and bucking at a canter makes me also think she might have an ulcer - my young horse did that when we moved him to the trainer and he got an ulcer from being away from home, in a stall, etc. Everytime we girthed him up or he really started working it hurt his ulcer and he acted like a beast. Normally this horse is a sweetheart and really tolerant so that was a big clue for me.
So, bottom line - rule out pain first and if it's not sore muscles, sore belly, or sore back from a new saddle, then you probably have a respect issue. The cure for that is time on ground work. There are a lot of threads on HF about that. If you're new to ground work, it's a good idea to check out the methods of some of the trainers like John Lyons or Clinton Anderson or Ray Hunt (deceased). Getting her attention and respect doesn't require force or punishment; it is based on pressure (asking for a behavior, like lowering her head or moving her feet) and rewarding the try. Good luck!
Edited - APHAforlife posted right before me - agree with all that he/she said!
Last edited by Ladytrails; 03-15-2011 at 08:39 PM.