My boyfriend and I have some different ideas about spending, but we both LBYM and prioritize saving overall. I've educated him about 401(k)s, health savings accounts, the existence of the Roth IRA, and many other things. The difference in us isn't in our financial or long-term ideas but in our personalities. I'm more cautious, he's more impulsive. That reflects in how we spend our money. I think that, somewhat, we end up meeting somewhere in the middle. He would go out for breakfast, coffee, lunch, and dinner every day of the week, but I've convinced him that cooking isn't *so* bad, coffee at home is more convenient, and compromised to going out or doing takeout food once or twice a week for dinner. It took him a while to come around on some of these things, but he does now see the value in eating breakfast and drinking coffee in his pyjamas.
It's quite possible that your girlfriend falls into one of the following statements:
(1) She doesn't know that she's living above her means.
(2) She has an impulsive personality and needs to be coached to think more about the future.
(3) Her friends are not frugal and yours are. That makes a huge difference in your habits.
(4) She is more outgoing than you. It *can* be harder for more outgoing people to spend less since they like to socialize outside of the house and that seems to require spending money to many people.
(5) For all you know, she saved up for that Cartier handbag for months and/or years and she'll keep that Mercedes car for many years to come.
How long have you two been dating? Have you talked to her about these things at all? Does she have a budget? Does she save for retirement?