Where Do You Put the Third Martikov Gem?

Hello! I'm a DM and I've run CoS once before and am about to again.

I was curious where you/your DMs have put the third gemstone that was stolen from the Wizard of Wines winery; if any thought was given to it at all in your game.

The first time I ran CoS I put the gem inside Vasilka as her heart/animating force. I was hoping to make may players have to choose between saving her life (they had grown attached) or gaining the Martikovs' trust. They chose Option C, because of course they did, and basically convinced the Mortikovs to adopt her and see if her presence would be enough to restore the vineyard. Later when they visited, I had her basically become one with the vineyard and be absolutely loving it.

I'm thinking of putting the third gemstone in Vasilka again for my other group just to see if they handle it any differently, but part of me wants to change things up for my own amusement. I'd love to hear your ideas and stories, thanks!