It's probably more about lack of liquidity than the lack of knowledge. Housing costs are higher if you are living in a daily motel and can't afford to pay 2-3 months of rent in advance. Food is also more expensive if you don't have access to proper cooking utensils and your own oven and so on.

It was a long time since I read the book, but I recall that the experiment ended because she had more unforseen expenses than she could keep up with. I think her car broke down a few times and as she had no money in her pocket, she had to take out payday loans to get it repaired. Eventually she couldn't do that anymore so no car, no way to get to work, no job and no income.