Give that lady an earful! I'm very non-confrontational as well, but if my horse refused to take the bit without a treat after she "showed me how to bridle", I would be yelling at her. And swearing. That is completely unacceptable. Tell her off next time you see her, be brave. At this point she is negatively affecting your horse and that is NOT ok, even if she gets mad, do you really care if a person like that likes you? I wouldn't. After that, if she ever offers any more unsolicited advice, ignore her. Give her the cold shoulder. If she says "Let me show you how to ____", cut her off and say "thanks I'm good" or "no thanks" and just walk away.