I suggest that the reason that the item is staying in Texas on display at the San Antonio Museum of Art for about a year is that it's going to take that long to complete the paperwork to export it to Germany. It has to pass through a bunch of restrictions related to traffic in antiquities (looted or not), it has a value to be determined for import/export that's potentially going to require duty payments, ownership is not totally established so everyone who touches it needs some sort of indemnification in case someone claiming ownership shows up (even if they are just chancing their arm), and it'll have to be insured. Unfortunately I don't believe the thrift store receipt helps any - otherwise thrift store receipts would be a fantastic tool for e.g. money laundering. It would have taken her and one or more specialist lawyers to get to the stage where she could safely hand it to a museum. I'd expect her to be considerably out of pocket in time and fees. It would make an interesting plot for a movie if you imagine someone trying all the naive approaches and triggering all the things that could possibly go wrong.