I'm sorry, but that's disgusting. If it were a $10 bag from a thrift store, a stench might be OK, but it's a $700+ designer bag. It's not your fault she lives somewhere the humidity runs down the walls; if someone wants to sell on eBay it's their responsibility to either take good care of the stuff (dehumidifier anyone?), or be honest about the condition in the listing. This just steams me!!
No wonder she's upset that you posted here. You told the truth, and that's going to cost her a lot in sales. I just ADDED her to my favorites list, with a big note that says "do not buy from...stinky & rude". I hope you (or someone) reported this to MyPoopers too because they really need to start cracking down on their "approved sellers". They have lost a lot of credibility with me over the last two years or so.
But most importantly...I am sorry this happened to you! I hope you can get the smells out of the bag, and that you are able to wear it and enjoy it in the future!!