The degree to which we can use Jack Maggs by Peter Carey to supply evidence concerning women's roles in London in the 19th century is rather limited. Peter Carey (born in 1943) is a modern Australian novelist, primarily concerned in Jack Maggs with moving Australia from the periphery to the center of a fictional universe created by Charles Dickens in his novel Great Expectations. Moreover, even Dickens himself recounts only a limited and fictional part of the issue; his work is intended as entertainment rather than sociology.
The role of women in Carey's imitation and Dickens' original text was highly stratified by wealth and social class. In Dickens, Miss Havisham is a powerful figure in the novel precisely because she is wealthy, and her power over Estella has to do with Estella being her ward and a generational difference. Even so, in the case of Miss Havisham, her wealth was not earned but inherited. It is also notable that as a female figure who is not subordinated to a male, and wields power independently, she is generally portrayed unsympathetically.
Ma Britten in Carey's novel is an enterprising lower class woman who sells abortion pills and is almost an archetype of the evil crone. Mary and Lizzie, although placed in a 19th century setting, are both improbably independent and display moral attitudes and a degree of freedom that would have been, at best, highly improbable in the mid-nineteenth century.
Although we can deduce from Carey's work that women were generally in a subordinate role in 19th century London, and that middle and upper class women only gained power through money inherited or acquired by marriage, in general, Carey is often quite unrealistic in his portrayal of women and not really evidence for either the real roles of women in the period or even how women were portrayed by actual 19th century novelists. For that, Dickens' original work is much more informative.