I'm not defending this woman's choice in boyfriend, but that is a bit pie-in-the-sky for me. Or 'let them eat cake' or something along those lines. I'm a working mother and while I have the benefit of a good husband and loving parents/grandparents, not everyone is working for a little extra pocket money so they can go to the movies. Life happens, and you could be one financial catastrophe away from having to get a 'part-time job.'
I've said many times before that if something was to happen to my husband, I'd not introduce another man into their lives until they're out of the house. I know there are great guys out there, but humans are, at their base, animals and many male animals have a compulsion to destroy offspring of other males. It's biology, and I don't think many humans are that far removed from that.
However, that doesn't mean this woman ever saw signs of abuse. Maybe this is like the shaken-baby scenario where the husband/BF never abused the child until he just snapped. Perhaps she had no clue about the sex charges. Doubtful, I realize, but while there are a ton of cases where I'll advocate locking the mom right up with the BF, I just don't think we know enough on this one and blaming her for working is really making the issue about something else entirely. This monster could have killed this baby while the mom was taking a shower, or having a nap. Outside gardening. The mom's job didn't kill this baby. Her waste of air boyfriend did.