It's smart to get the receipt with weight, you are covered. Of course, Tradesy as its their label and their responsibility will take some time to investigate. What I know it's about 2 weeks with UPS, should be similar with Fedex. After that time you should start bugging Tradesy to release your funds. It's Tradesy's problem to deal with the buyer, not yours. They can remove her account, file criminal charges, whatever. They are intermediaries and take a hefty commission for that to deal with issues. As for buyer, I don't like the story how she was out of town and the neighbor involved, then "box is empty". Could be a package pirate took it from the box, but you know what, I wouldn't buy if I know I'm going to be out of town and the box would be sitting on the street. Too many red flags.
And I'm like you, selling mostly high-end items and I have seen it all. Most recent one was "someone else charged my card but delivery address was mine". What's the point in that? To steal her package before she'd pick it up.