For the shipping, if she had the shipping cost posted in the auction then I dont see a big problem. If you didnt like the costs, then you should not have bid. If she charged you after and still overcharged you, then that is just wrong.
As for the feedback, I agree. DO NOT leave her feedback. I would give her a neg and take one before I let her get away with that. You can also follow up on feedback if she gives you a neg and explain to people that it is a retaliation neg. What a bootch.
Please let us know what happens.