Mimi is a very minor female Peanuts character who has never appeared in the strip, but appears in the TV special, It Was My Best Birthday Ever, Charlie Brown. Linus becomes attracted to her because of her beautiful singing voice. She is staying at her grandma's house for a week when Linus meets her. She teaches Linus about flowers, telling him that she finds flowers fascinating. Linus invites her to his upcoming birthday party.
Linus cannot get her off of his mind. He constantly thinks about her and her beautiful voice. She does not show up at the party right away, which makes Linus very anxious. At the end, however, she does show up, sings "Happy Birthday" to Linus, kisses him, and hands him a flower before she leaves.
She was voiced by Jamie Cronin, who also voiced Lucy van Pelt in the same special.