I agree, Toddlerteaplease. I'm surprised your friend got maternity leave. Was it actually unpaid leave? I didn't think there was any right in law to maternity leave until the 1970s. I had teachers at secondary school who left towards the end of their first pregnancy and never came back, and that was the norm. By the later 70s the odd one did return after maternity leave, as was their right by then.
My impression is that before the 1960s working class women were likely to have extended family around them who could look after their children and that always made it possible for them to work in factories, cleaning jobs and so on. Their families had pressing need of extra money so of course they worked when they could. I was really surprised to read that statement of Jennifer Worth's that the married women of Poplar didn't work, but I can't see why she would have got that wrong.
When it comes to office jobs or anything needing professional training, it was understood that some women with children would have to work - widows, divorced or separated women, women whose husbands were invalids or disabled. They could get jobs, but of course were paid less than men doing the same work. Many employers would otherwise have actively discriminated against women with children, or even just married women, to protect employment opportunities for men, who were seen as the breadwinners. And of course many men forbade their wives from working outside the home. 
A tiny number of women were so talented that their employers, or if they were self-employed, their clients, would bend over backwards to make it possible for them to continue working. It would have helped a lot to be very well off as then the cost of decent wraparound childcare wouldn't have been an issue. I'm thinking of high profile journalists, actresses, designers and so on.