Always keep in mind guys that women are the gatekeepers of sex and men of marriage. Mostly women benefit of wedding.
So my advice is:
If she wants to get married than I am the one setting the rules and not her. Her family can't be not okay but just wait a few years until she is older because remember... The wall is still undefeated.
And, actually a Thai girls family with only the passport she gets when married and the social benefits from that should pay us not the other way around. If she marries a Farang there shouldn't be sinsod, ever heard of a Thai paying it to the Farang brides parent?