Hey flipper,
That sucks. I'm sorry. I've been in similar positions myself, and it doesn't feel good.
Just drop it. The chair knows it's a sh!tty situation, and that's why she's being cowardly and ignoring your emails. She probably didn't take the course just to be nasty.
The way I viewed part-time/adjunct positions is that I am "using" them--to get teaching on my CV, to get favorable observations/student evals, and to get references. Any future job you take will want to contact this woman, so make sure she doesn't think negatively of you. Only behave in such a way that will benefit you and your career. So I would keep my name on the list for now, but look elsewhere.
Oh, and check out this thread of you haven't already. It won't help the situation, but it may lift your spirits:
http://chronicle.com/forums/index.php/topic,44416.0.html