@WillTell
two things.
1) she didn't know the artifact was only useable by one person
2) she didn't know whose hands were part of making a devine tool
I'm always a bit generous with manga adaptations as things may be left on the table, but I assume that making contact with a god isn't exactly the hardest thing in the world if you have the right methods, and only members of the temple generally want to make contact, or can make contact.
She wants to take the artifact because till then its of unknown origin, but it is in the hands of an outsider and she couldn't bring him into the fold.
Its not really stupid, in fact if it didn't go this way it would have been weird, the the fact she took everything at face value and backed down when cards were shown means shes not dumb.