We can now confirm that Hilda can be recruited outside the Golden Deer. If you are playing in the Black Eagle Route, you can recruit her between the time after Edelgard reveals her true goals, and before the timeskip.

Can Hilda join Blue Lions?

How to Recruit Hilda. Hilda is the bodyguard of Claude, and as such cannot be recruited from the Golden Deer House while you are in the Black Eagles House. However, if you are in the Blue Lions House, the restriction appears to be lifted, and Hilda can be recruited.

What is the best class for Hilda?

Unless the plan is to make her a Warrior with a high crit rate, Hilda should learn flying as soon as possible. Wyvern Lord is one of the best classes in the game because of its wide-reaching stat boosts and growth rates.