Owe, baby, baby
My girlfriend always cries that she's "broke." I just ended up buying her groceries and paying to have her car fixed, and then I discovered by accident that she'd recently paid hundreds of dollars for hair extensions, beauty products and a facial. She isn't the first girlfriend I've had who prioritizes beauty stuff over necessities. I really don't get some women's relationship with money. — ATM on Legs
Some personal financial crises are caused by unexpected events, and others simply by how one answers certain basic questions, such as "Hmm, get waxed or continue living with electricity?" or "I can't decide: New brakes or traffic-stopping hair?"
Old-school economists, who view humans as hyper-rational data-crunching machines (like big, sweaty chess-playing computers), would tell you that it makes no sense for your girlfriend to keep ending up, as the saying goes, with so much month at the end of the money. (And sure, car trouble can pop up out of nowhere, but it isn't like the need to eat comes as a surprise.)
Evolutionary economists take a more nuanced view of human rationality. They find that our glaringly irrational choices in one domain (like the survival domain, including financial survival) aren't so irrational in another (like the mating domain). For example, because men evolved to have a very visually driven sexuality, women looking to land a man or retain one's interest will (often subconsciously) prioritize beauty measures — sometimes buying eye creams so pricey they should come with power steering and a sunroof.
And though we aren't in a recession right now, a July/August 2014 Public Religion Research Institute poll found that 72 percent of people believe we are. This is relevant because research by evolutionary psychologist Sarah Hill finds that though economic downturns lead both men and women to cut their spending across the board, they also seem to prime women to increase their spending in one area: beauty enhancement. Hill explains that a scarcity of resources appears to cue an evolutionary adaptation in women to "increase the effort they invest in attracting a mate who has them." (And this seems to be the case even when a woman has resources of her own.)
Still, it isn't fair for your beauty-bingeing girlfriend to treat you as her boyfriend-slash-overdraft system, taking advantage of how you'd rather pay for her car and groceries than see her hoof it and crash wedding buffet lines with a big purse. Tell her that you feel bad being put in this position and though you love her, her abusive relationship with her debit card is eating away at your relationship. (A mate-retention warning light should go off in her head.) Next, show empathy. Mention that many people find themselves in her position, mainly because nobody ever taught them how to budget, and we aren't all natural fiscal wizards. In fact, we're more like chimps with credit cards.
To help her conscious mind better understand her subconscious one, explain the evolutionary view of human rationality and offer to help her plot out her finances. You might get her the book Smart Women Finish Rich by David Bach. And because our decision-making ability evolved in an ancestral environment where we typically had just a handful of visible choices in front of us (like five bison and one with a limp) — as opposed to big mathematical abstractions to chew on — you can help her get a better grip on her spending by making it visual. As for how helpful visuals can be in decision-making, evolutionary cognitive psychologist Gary Brase finds that people are far better at understanding medical risks when they are communicated with pictures (for example, 100 little people on a page shaded to show that this many of 100 will be cured and this many will end up going home in an urn).
In keeping with Brase's findings, you could draw little rectangles all over a page to represent $100 bills (in the amount of her monthly salary). Color in blocks of dollars to indicate all her monthly expenses, including any potential expenses, and offer to help her budget until she gets the hang of it. If you're open to paying for the occasional item that's not in her financial plan, let her know, but explain that you'd like to be asked first, not just informed that all of her dollar bills have run off and taken up residence in the cash register at Sephora. And finally, while you're helping her tally things up, you might take a moment to count your blessings. Your girlfriend might be a little money-dumb, but she seems to understand the importance of keeping up her curb appeal — mindful that there's a reason men get accused of talking to a woman's breasts and not her calculator.