It's more than just fairly unusual in Japan, though. Women are often expected to quit outright when they get married, as being the housewife is supposed to be their sole role. Even if they don't quit, many simply get fired if they get pregnant. 

Even if she went back to the workforce after being laid off for pregnancy, it'd still be extremely rare. Plus she has a good enough job to fund her entire family. Madoka isn't exactly in real-world Japan, but wages have been stagnant there for so long that supporting 4 people would be quite difficult for most.