But how did the mother get into position where a) she's single and b) she needs to work 3 jobs to get by?
One situation is teen pregnancy. Say a girl gets pregnant as a teenager and the father flees (common for single moms). Now she has to raise a kid by herself and drop out of school, limiting her career options.
Is this an individual responsibility fail or a societal fail? I guess you could argue "society failed by not providing her with free contraceptives and/or abortive services and/or social services" but it's just a bad, sad situation no matter how you slice it, and clearly there was some personal agency involved. Even worse, it's a self-perpetuating cycle (i.e. the pregnant teen's offspring is more likely to also be a pregnant teen)