Who is Slumtrimpet, the devil in charge of the patient's fiance from The Screwtape Letters and what is their importance?

Slumtrimpet is a female young devil. The lilting "trimpet" suggests someone light of step, while the "Slum" suggests where this person abides spiritually. She is in charge of the young woman the patient falls in love with. She does not seem to be having much success in tempting the young woman into any kind of serious sin.