One if the best descriptions of the plight of the middle class woman is in hodgson- Burnett 's Emily Fox Seton and The Making of a marchioness, published about 1901, where it is clear that for a not v bright uneducated poor middle class girl the chances of marriage were slight and she could therefore become a companion, lose status and become a shop girl or servant, or starve. And the long term prospects were the workhouse or starve. It's explicit in the sequel.
It's a bit earlier and of course WW1 had in theory opened up more careers for women, but in practice employers generally wanted to employ men in part because they recognised that the men would often need to support a family, whereas they didn't assume the woman would be a sole breadwinner.
I recall my mother explaining this to me; her father ran a business, was not at all misogynistic, had a social conscience. I think he may have had about one female clerk who was unmarried.
Given Garnie's abilities, she actually does the right thing with her capital. After all , the Wall Street Crash had happened so investing house sale proceeds could have been disastrous. We are also told about the crash in rubber, Mr Simpson loses his job. Garnie's just not very good at managing..Petrova would have been better.
But I always think it's a shame they didn't put Petrova in for a scholarship.