I totally understand this girl i feel the same way sometimes, but for me, i dont know if the same for her, i know the reason comes from too much exposure and thinking like the non jewish world, where ppl dont want to commit, and its easy to think that one would have a much easier and more fun life without being tied down to a husband and children, and all the responsibilities it brings, and the fact that u are not free to do wat u want and have fun in the same way u did wen u were single.
Looking from a secular viewpoint, which is what a lot of frum young ppl do whether u admit it or not, married life is totally not worth it, it feels like were wasting our young and best years, being married, and unable to party and have fun.
Obviously having fun in a wrong way, but thats not the point.
I dont know if this is the reason for the girl u are talking about, but if it is, and im sure there is some of that mixed in, what helps me is going to shiurim, reading english seforim by rabbis, and listening to real jewish music, basically trying to immerse myself in jewishness and then it helps you see the truth, but its hard.
Anyway all im saying is that its normal, and all you can do is try to inspire her with yidishkeit, and talk to her on a deep level etc.. I hope im making sense..