Why doesn’t the woman have enough money at hand to rent a bigger house?

M: Welcome to Philadelphia, Julia.
W: Thank you.
M: Is everything settled?
W: Almost.
M: What can I do for you?
W: I suppose I should look for a bigger house. But I don’t see how I can afford one right now.
M: If only you hadn’t spent so much money on your vacation this summer!
W: You’re right. But I really had a happy vacation.
M: OK. Maybe you can move into my mother’s house and share that with her for a couple of months.
W: Thank you. But I don’t want to trouble you too much.
M: No trouble at all.
W: How much should I pay for the rent?
M: About ＄400 a month.
W: Great. That’s one-third less than it was when I first rented a house.