Di7

Maybe she wants to know him enough to make him "have an accident"... heh. Seriously though, saying she's the box owner won't work because it's VERY unlikely the azzwipe will let her leave before inspecting the box's contents. Moreover, they would probably demand that she prove she is the onwer by opening it (as the owner would have the key or know how else to open it), and even if she claims she lost it or never learned how to open it they would say they still need to confirm that by checking the box's contents.... Then, when see the marriage contract, they'll either figure out who she is, or accuse her of lying about being the owner in order to steal the "prince's missing wife's" belonging the first place (they might even demand to know if she "stole" the box because she knew what it had inside, and if she'd been tasked with stealing it for someone else, someone more powerful who would have wanted to get ahold of the prince's so-called "weakness").

With the amnesia thing, at least, she can buy time and find a way to escape at the first opportunity they get distracted, as they would have to let her be while they're investigating who she is, and what her relationship is with the box's contents.

Alot of problems for just a box lol..
but true yeah i thought about it after writing the comment
And Especially if the box has her family logo or idk what it's called on it
But that asshole of a prince and his audacity