It's not like getting married means she drops out of school to become a housewife or something like that. Getting married young isn't the worst thing, to them it just means relationship stability. One less variable. "Of course we aren't gonna fight or break up, we're married."

Of course, that's in theory and in practice may go differently. But I got married young and it's working out well for me. It's the one aspect of my life that I don't have to worry about. Working as a team makes them stronger as a unit financially and it makes it easier to plan your adventures in life, figuring out where you want to go and what you want to do after graduation, etc. If the worst that happens is they end up divorced and she learns a thing about life, it could be worse.

At the end of the day, she's her own person. You can't tell her not to and any opposition will just drive a wedge between you, which might make it harder for her to get out of her situation if it ever goes south and she becomes isolated in her relationship. She won't reach out to you for help because she doesn't want to hear "I told you so".

My advice would be to encourage her not to have a huge wedding because they are young and it is expensive. You could suggest that they stay engaged until they save up enough for the 'wedding of her dreams', tell her that "You only do this once, remember?". That could potentially delay the wedding by a few years.

If she does just decide to just haul off and get married the best thing you can do for her is love her anyway. People make mistakes. You can't stop your kid from making every mistake, you can only be there at the end of it to help them back up and hope that they learned from it.