
Hi
I have a collie GSD cross. Mine is a small collie sized black and tan version.
I suspect that your dog is not at all a dominant dog. In fact, she seems to me from what you say, to be very very nervous, and insecure.
If she has found that snapping or biting/growling at the things that scare her work, in that the offending person backs off, then she will do it again.
If she is being put in the position where she feels she HAS to take the dominant dog role, then she will feel under even more pressure, which for an underconfident, nervy dog, will make things far worse.
You need to watch how your dog behaves a lot. If she truly was a dominant dog, then you would not get any sense of her being nervy or scared. Check out her body language, does it seem confident? I suspect not.
What you will need to do, is to make sure she understands that YOU are the boss. I dont mean in a harsh way, you make the decisions, and you will protect her, and not the other way round.
Give her another option other than fighting, snapping, etc, ie, teach her to hide behind you if something is scary. Dont push her into situations you know will frighten her. When you have worked out all the things/situations that scare her, then you can work on improving her confidence more.
You really need to limit the times when she will be scared, and keep good control of her, as the more times she has to resort to using her teeth, the harder it will be to persuade her that she doesnt need to.
Good luck,
Emma