Technically, she hasn't done anything wrong yet.  Baypal will take that angle.

Even if you had contact with other Sellers she has purchased from to prove/disprove her scamming ways, Baypal would still wash their hands of the matter.  It would roll over into the real legal world as fraudulent activity I'm afraid.

For the few things I've sold, I made videos of me packing the items and if it involved some measurement, then I could make that clear in the video as well.  As a Seller, I think like a Buyer and ask myself how could I make a claim against this - hence the videos.

I'd also show the mailing label up close, and then affixing it to the package.

There was one item that I simply put in a red roadside aussie post box rather than drive into town.  I even made a phone video of me doing this.  That was handy as that item 'never arrived' ... well, it definetely left.

Anyway, perhaps contact other sellers she made purchases from (if possible) and spread the story.