Absalom's lady friend shares some characteristics with Gertrude, Kumalo's sister. She has had a number of different boyfriends, none of whom were actually legally married to her (though she refers to them all as "husband" [1.16.55]). She is also a runaway. However, in spite of her sexual promiscuity (or freedom, depending on how you want to look at it) and her decision to disappear into Johannesburg, Cry, the Beloved Country appears to judge Absalom's fiancée much differently than Gertrude.
Why doesn't she get as much criticism as Gertrude does for her sexual desire? Well, first of all, Absalom's girlfriend comes from a broken home. Where Gertrude fails to fit in with the morally rigid household of her preacher brother, Absalom's girlfriend runs away from home because her mother drinks too much and she can't get along with her stepfather. Gertrude chooses to abandon a perfectly good, decent life (according to the morality of the book), while Absalom's girlfriend has less choice about seeking out somewhere else to live.
What is more, the girl's series of boyfriends don't sleep with her for money (it appears). They do not disappear from her life because she's unfaithful or anything like that, but because they all get arrested. Absalom is the third in a line of men she's lived with who have been thrown in jail, which isn't really the girl's fault.
But the biggest reason that Absalom's girlfriend seems to escape the moral criticism that Gertrude receives is for the same reason that Absalom does not receive the ethical blame that John does: she is a completely passive, empty character. Again, like Absalom, the novel portrays her as symptom of the broken families in the black communities of Johannesburg, rather than as a cause of these troubles.
Honestly, Absalom's girlfriend's total happiness to go along with whatever Kumalo wants is a little unsettling to us. Shouldn't she have some wishes for herself? It's as though the novel is suggesting that the ideal woman should essentially be seen and not heard—and maybe not even heard.
After all, this girl is a pretty important character—the daughter-in-law of our main character, and the mother of his future grandchild—and yet she has no name. She receives moral redemption from the novel because she has no desires of her own, while Gertrude's active wishes receive regular criticism from Mrs. Lithebe and Msimangu. It's as though the only way a woman in this book can have an actual personality is if she's morally bad.
Perhaps the biggest sign that the gender politics in this book can be a bit wonky comes when Kumalo first talks to the girl after visiting Absalom in jail. Kumalo grows angry with her because of her sexual history. He demands to know if she would sleep with him if he wanted it. And she is clearly freaked out but she laughs nervously and says, "I could be willing" (1.16.74).
Kumalo is horrified with himself for bullying her in this way—and he should be horrified, since he is her child's grandfather (ew!). He does not actually sleep with her, and he apologizes for his behavior. But the fact remains that this whole scene proves to us that the girl is quickly intimidated and coaxed into sex. She is young and easy to influence, either for good or bad.
Indeed, the novel continually reminds us that she "was surely but a child" (1.16.11) (which makes her pregnancy even more deeply unsettling). When Kumalo asks her if she would be willing to settle in Ndotsheni, she is thrilled. She assures him: "Quietness is what I desire" (1.16.92). Unlike Gertrude, whose desire is sexual in nature, Absalom's girlfriend has no wish but to live meekly, without making trouble.
The girl's passiveness seems to suggest that (a) the novel doesn't hold her responsible for behavior that it generally finds wicked, or in other words, for sex outside of marriage; and (b) that the girl is going to be a good daughter-in-law to Kumalo because she is absolutely obedient and will do whatever he tells her to do. We're supposed to believe that Kumalo, as a good man, will not abuse her faith in him (again). But this absolute meekness on the girl's part strikes us as a little hard to take in this more feminist day and age.