Since I really think this could be a big power change to Eva and would certainly impact other magical weapon users and I don't have access to Discord. Let me try and be clear about how Eva's affinity with Magical Weapons works. 

Let's continue to use Thors' Hammer. Any weapon that can be owned either due to spell or spirit attached to it. It will depend upon the owner how long she could use it. Say If Thor was cool with Eva tossing around his hammer she could essentially use it as long as he sees fit.

But if it is owned and the owner wants it back it will resist until she is no longer able to wield said weapon. Although how it returns is a whole other matter. Though Eva wouldn't just keep anything that doesn't belong to her unless the owner is totally evil and she doesn't want it to fall into the wrong hands.

Then the only way would either be to kill the owner or break it's spell with help. Say Alternative Merlin.

But again no OCs need to worry about Eva pilfering their weapons. Since she's good. These are just ideas about how it could work. So let me know how this looks.