Since I can't browse the internet to check the latest updates, I'll have to rely on existing knowledge. Stardew Valley does have mods where players can create custom structures like alcoves for their partners. The Flame Princess has her own mod or is part of a mod that allows her to live in an alcove. "Polly" might be the creator's name or a specific version of the mod. The "Alcove 2" could indicate a second version of the mod.