bnwt, she sounds like a true horror.
Of course, she probably doesn't realise what she is doing; have you noticed the tendency of very aggressive and critical and "the world owes me a living" type of people to believe themselves to be in the right, while everyone else around them is in the wrong?
Whatever is causing her snapdragon behaviour, you obviously gave her great service. You pegged her for the type of person she was, and still gave her the best service possible; you gave her a full refund while knowing she'd still neg; you went over and above good seller behaviour.
Good to hear you got the negative removed. I have a weird mental image of your rep trying to phone her, her hanging up twice, and then after she'd hung up, there she is on Twitter, writing "eBay rep very tacky. Hung up on him. BIG NEG!" ... (Good lord, she might even be doing exactly that...)