I don't like
Millicent (I think it sounds fake, formal, and mealy) and I guess
Millie is cute but sounds like the name of a small dog.
Millicent Marie is too cutesy and matchy.
I like
Melisende.
(What even is the deal with
Millicent? There are so many cooler names you could have gotten from
Amalaswintha. Amasintha, Malaswin, Malasintha...)