5-year-old troubles

Question
I have a 5-year-old filly that's green broke and a very fast learner, but she's recently developed some habits that I worry about.  
-She bites when I sinch her saddle
-She bites when I work with her feet
-She bites when being led and pretty much any other time she feels the urge.  
She's never done any damage, but I'm getting worried.  How can I teach her to stop biting?
Also, I'm only begining to ride her again.  I haven't actually sat in the saddle yet, but I've leaned over it and such, getting her used to my weight.  Still, she seems to be very nervous and high-strung as soon as I get in the saddle.  I want to teach her to be calm since I've been bucked off her many times(I broke my arm and my tail-bone the last time), but she seems simply afraid.  I don't want to push her, because our whole relationship is based on trust and keeping just at the borders of her comfort zone, so as to widen it, but she's never taken this long to understand that I'm not going to hurt her.  Could the fact that she was broken at 2 have something to do with it?  Could I be doing something wrong?  Do I need to take a different approach to teaching her?  
Any advice would be greatly appreciated.  Thanks!
~Andi~

Answer
Dear Andi,

I apologize for taking ages to get back to you. We have been away horseshowing. I read your letter and am concerned you are going to get hurt. Your filly first needs to understand biting is absolutely out of the question. That means you are going to have to give her a terrific slap the next time she makes a move. If she is doing this during cinching remember not to crank up the girth tight when you first put the saddle on. I would normally tell you to check the fit of the saddle and make sure she isn't in any pain. However, I have a feeling she is being naughty more often than not. So......I think this is a behavior issue and not a way of asking for help.

Maybe you should send your horse out to be started back under tack with a pro. It often does a young horse a world of good to go away to school. They learn to travel and more importantly they learn to adapt. I appreciate your love and compassion for your filly, but I think she is taking advantage of a kind soul. That's what young horses do. I guess it's sort of thier job in life. (just like teenagers) Just like teenagers they need discipline and a schedule. This is where a pro can fill in the  blanks. They aren't emotionally attatched like parents are. They can see things from a different perspective. If this is too expensive then have a pro give you some lessons. Make sure you use someone used to working with youngsters. You don't want to ask too much too soon.

I hope this helps and I haven't rambled on too much. I've been in the sun all day and the air conditioning is making me giddy. Good luck. Feel free to let me know what you come up with.

Warm regards,
Shannon