The duchess, poisoned after accepting the invitation.
Invitation from Her Majesty Empress Delilah Kaldwin is a written note found in Dishonored 2.
Transcript[]
To the Duchess Lucille Clothilda,
I hope this note finds you in good health. Yours was the first such correspondence offering me fealty, and officially denouncing the murderous Emily Kaldwin. Swift actions such as yours deserve reciprocity.
Come join me for a dinner in your honor. My kitchen will prepare jellied oysters, herring in gravy, and some of those unusual Morleyan clams that thrive only in brackish waters. Let it be tomorrow evening. For I am eager to show how I feel toward one who is so quick to change allegiance.
Location[]
The note can be found on the dead body of Lucille Clothilda in a lavatory near the top of the stairs to the security room in Dunwall Tower during the mission Death to the Empress.