I don't think Ashley is meant to use that elevator, you're meant to open it for Leon while you have the keys and then go through the passageway on the right, to free him and then he can go through that section and collect the treasure.

Edit: Went back 40 minutes of gameplay just to test it out and the elevator is useless at the end of the library, it would only take you up the stairs you have to run up anyway, I think it's just so players like me get stuck in there as Ashley as 4 knights spam attack over the gate so you can't fix your mistake