It doesn't matter how much money you bring home: it's essential to keep a budget. I'm not one of those people who writes out exactly how much I'm going to spend on every expense, though that's probably the most optimal way to budget. I subtract savings, investments, rent, and utilities from my monthly income, then divide what's left by the number of days in a month. This gives me a daily spending limit. This system isn't perfect, as I often spend more on food than I should, but it works for me for now. It's much better than what I was doing before, which was barely saving anything and just making sure I didn't go below a certain number in my checking account.
If you're keeping some sort of budget, you know it's not inherently nefarious to spend money on something you want. If you have enough money to buy new clothes every month, you can include that in your budget and feel confident you aren't using your grocery money on an unnecessary item. Every single one of us spends money on something you don't technically "need." If you ever go to Happy Hour, you're spending money on something that you don't need. Somebody else might think that's frivolous, but to you, that might be worth the $15 you spend.
When you're a single adult, nobody can tell you what to do with your money. You could spend most of your disposable income on mochi, and nobody could tell you not to. It might not be a great idea, but you're free from your mom telling you not to and your spouse telling you not to.
When you're dating somebody, and you're not yet married, they really don't have a right to tell you how to spend your money. The woman in this story doesn't understand that; she's trying to control how her boyfriend spends his disposable income.