Combining the mild and the innocent, this sweet and feminine name is worthy of a comeback, in the mode of Madeline and Cecilia. Its original, also attractive form is Melisende.
Millicent has been in use since the Middle Ages, and was in the Top 500 in the 1920's.
Millicent Hargrave is a character in Anne Bronte's The Tenant of Wildfell Hall and Millicent Henning is found in Henry James's The Princess Casamassima, and she appears not once but twice in Harry Potter; she is is also Barbie's middle name.
And of course Milly is one of the cutest of the nostalgic nickname names. .