Both my wife and I are far more frugal than our parents. And yet, both of our parents are very well-off financially, because they have always lived below their means. Both sets of parents still have mortgages and car payments in their '50s. My dad even took out a $12,000 loan to pay for my sister's wedding, yet he paid for his $25,000 workshop in cash. My dad managed to retire before 55, and my wife's parents will retire by 60. I don't understand why they do what they do, but they are doing what works for them. And my wife and I are doing what works for us, which is saving madly for early retirement.
In other words, don't judge this girl too harshly based on her parents. She is not necessarily of the same mind, and even if she is, it doesn't mean she is not willing to change. Some people are naturally frugal (like my wife), and others just need concrete goals for serious saving to be possible (like me). I didn't become a serious saver until I was presented with the possibility of FIRE, and it immediately turned my finances around. I haven't looked back once.
So like the others said, get to know her better, and talk to her about it.