So I only just realised that Rosalie actually has the detect secret doors ability! However (and I don't remember), I think she leaves after completing the Bandit Caves, and you can't re-hire her once she leaves, and the Bandit Caves is the first dungeon in the Act I sequence? Completing the Caves leads Maximus to ask you to complete the Lighthouse, and completing the Lighthouse leads to Castle Portwhatever. You can't even enter the Castle until Maximus has given you the quest. So I'm not sure how you can keep Rosalie for the Lighthouse & Castle, because you have to complete the Caves (and lose Rosalie) before you can do either of those dungeons?