Janet is Miss Betsey's maid at her cottage in Dover. She is a sensible, neat, pretty girl of about nineteen. Janet is the latest in a line of girls Miss Betsey has employed "expressly to educate [them] in a renouncement of mankind" (13.111). In other words, because Miss Betsey has been so unlucky in her own romance, she's trying to train girls to give up all thought of men at all.
Despite this anti-man training, at one point, David says that Janet winds up marrying a baker. At another, he says she was engaged to a pilot but doesn't marry him – not because of Miss Betsey, but because she doesn't like the guy. At any rate, it does seem clear that Miss Betsey's teachings have not strongly influenced Janet's fate.