Mildred "Mildew" Haversham is a major character within the Bad Machinery stories, making up one third of the mystery solving girls.Perhaps not quite as well-read as Shauna Wickle, she still has a great love of academic learning inherited from her professor father (Neil Haversham of the University of Tackleford), and is into adventuring, troublemaking, and gossip-mongering along with Charlotte Grote, though has more desire than the other girl to think things out and figure out if what she's doing actually makes sense.
Mildred has been raised in a "liberal, permissive" atmosphere, though such an environment does in fact have quite a few rules to it, including strict veganism. She doesn't necessarily follow anybody's rules, including her parents', when nobody is watching.
Sonny Craven is Mildred's first cousin.
She is working a summer job at a tea house, and tried unsuccessfully to get Charlotte to apply for a position there as well.