Actualy i think that would not require much alternation ...
I remember in some past patch, she said to me when i had the box something like "seems like it wants to stay with you ... okey, as long as you keep it, i will stay aswell" ...
Something like that could work ...
You take it > you have undroppable box ...
You dont take it > it takes itself.
Shadow wants it ...
So you can give it to her, and she stick around ... so you still keep it close.
Or you can not give it to her, and she will either stick around to watch you (it), or she try to persuate you if you have positive relationship ... or attack you if you dont.
And if she die, or you send her away somehow ... the item re-appears in your inventory next morning, just as it would if you ignored it at the begining ... and next evening Shadow can re-appear in your camp, wanting her box back and you dead so it stays with her this time.
(Just as The One Ring ran away from Golum.
)
Also ... i admit i really miss that
old psychotic dialogue you get when she ambushed you in middle of the night, bcs "voices keep bothering her, and something drags her towards you" ... it was much greater than what we have now.
