Ebay is a like a free for all, everyone has to watch their own back while using it. There's definitely great things to be found, but when it comes to designer items, you have to be extra careful. Always use a forum to check auth before paying, and once you pay, use CC, like AMEX. Paypal sometimes helps, so it's better to use that than nothing. Never use Western Union, bank transfer, wiring, or BidPay because you're not protected.
If there is anything on Ebay you are considering purchasing, if there is even only 1 flaw, don't buy it. You're better safe than sorry.
I'm sorry this has become a learning experience for you, everyone here has been through something like this before. I myself got duped on a
Gucci bag years ago before tPF came into existance. We all have to learn somehow.
My only last advice on your stam purchase is to call the police and file a claim, in your country and in hers. You have her information, correct? It's illegal to sell fake handbags, if you call and report it, the seller may be scared into giving you a refund. Can't hurt to try.