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

Hey, can you tell me, I can't sell unwanted artifacts in my own castles - is that how it's supposed to be? There's a button, but it's gray and inactive.

Also, will Lyudmila be in the next missions?
Is it worth training her in battles with neutrals, or is it enough to just have her run around collecting stones and protect the sea castle with its bonus?