I do NOT think you should meet up with her. It may be a long shot, but you don't know her or her acquaintances. She sounds "nice," sure, but the best cons always do, don't they? Maybe she is, but you just don't know.
Someone's scamming you here somewhere, and until you know you're safe I don't think you should be meeting up with them or exchanging any personal info. It could have been her SO or her family member that took it before she got home to sell it, or whatever, my point is they don't sound like people you know you want to be involved with. It's a lot of money, yes, but your safety is worth more.
To me this looks like somebody opened the box and took the bag out, plain and simple. I really, really doubt any postal worker would put a box in that condition into their truck, much less deliver it. They are responsible for it being delivered sealed, in the same condition they received it in. That's why if it's opened en route for inspection (customs, media mail, etc.) they put a notification on it explaining the situation.
I sure hope this works out for you. Hopefully the postal people can help you put these pieces together. I'd imagine they have to be able to vouch for it being sealed at the time of delivery, which should let you off the hook. good luck with this, i really feel for you~