if horse is also bucking on lunge line, this could be due to discomfort. I kinda think it's her just expressing her opinion, but if she's always been good to lunge before, but now is bucking at the canter, with or without a rider, then maybe saddle or back issue is a possibility.
All the things the mare is doing are not seperate things. They are all her carrying out her thought, ignoring your directions. How or where she bows out is not the point. IT's that she is not listening to your application of the rein.
She may just need to have you apply a bit of a spanking to get her to beleive that you mean what you say and you'll enforce it.
that, and if you can do groundwork where you move her around in various directions to get her listening to you.
if you've been riding fro 3 years without instruction, then maybe it's time for you to look into getting some. at the very least , look into some videos. If your friend hasn't been able to help you with this so far, she won't be able to. we can give a small amount of advice over the internet, but it's hard to really teach via electronic print.
Do you want to stay here, where you are with this (and it'll likely get worse), or do you want to put in the energy and find a real teacher and learn some new stuff? Either way is ok, it's what is fitting for YOU.