I agree with what people say here. N'Tina harm arai khaow mai dai, but as a friend, give her advice. She may be not listen to it now, but later she will understand what u meant.
Bork khaow wa karn taeng ngarn isn't like in fairy tales there r good and tough moments in every couple and that u are not trying to make her change her mind but u just let her see a few cliché of how life is when u are married (love isn't enough, there are also committments), that she shouldn't base her own relationship and future (professional and personal one) on your experience of that or only on her love feeling.
Each situation is unique, different, marriage can work well for some couples (old couples or young couples) as it can fail for some others.
Laew hai khaow kid dee dee, tob tuan took sing tee Tina pood lae sing tee tua khaow eng kid lae roo seuk, then it's up to her to make the choice. If she knows the goods n bads in marriage and is ready to accept it, then let her choose.
I think that's what u can do, not harm not aow jai chuay, but just give an objective opinion and also be present for her in the tough moments.
mai roo wa pood took reu plaow niaaaa, i mai khoei taeng ngarn loei lol...