I was thinking daughter or neice.
My mind didn't even go there. If Lilith was one of those, why was Bela haring off somewhere else with the gun and not right there with Dean and Sam? Besides, why would she need the gun to save her daughter, when her daughter is a demon? The only thing the gun could do is kill Lilith. I don't see it. I think Bela, as with everything she steals, is going to sell it to the highest bidder. And that is going to bite her right in the ass, because I'm willing to bet it's not a hunter.