Necropolis – “Dawn from All Sides” [Campaign 2, Mission 3]

Hey, can someone tell me if it's intentional that I can't sell unwanted artifacts in my castles? There's a button, but it's grayed out and inactive. Also, will Lyudmila appear in later missions? Is it worth training her in battles against neutral creatures, or is it enough to just have her run around collecting stones and protecting the sea castle to increase its growth?