> ... 7.5% of her income. That seems astonishingly low, to me.

You've fallen victim to presentism, the cognitive bias of assuming the past was like the present.

Before the 20th century, households spent a far higher proportion on their income on food and on fuel (for space heating, cooking, lighting) than we do today. Clothing and footwear also loomed large in the budget. Housing used to be a relatively smaller cost than these.

7.5% is possibly on the low side for the time, but not astonishingly so.