I read all the responses first and here is mine.
Do you feel the wedding has any chance of lasting? Do you think that boy is going to keep his hands to himself? I would not help my daughter marry this boy. She could throw a fit and I wouldn't pay a dime and my gift would be, as suggested, something personal that can't be redeemed for money, such as a nice, personalized "welcome" sign for the home. This marriage will probably last as long as the money comes and I'd want my daughter out of danger and home before the baby is born. This is a sick kid (him) and his family sounds sick too. I wouldn't bother with a long letter because difficult child's can keep letters, show them to others, and have others misinterpret them. I put nuttin' in writing...lol...unless I'm writing to myself only (yes, I'm crazy...lol). In two months, if you don't give her money, she'll be begging to come home. I would do nothing to sustain this sad relationship. This is not a safe partner for your daughter or her baby and it's kind, in my opinion, to do all you can to discourage it, even if she initially feels you are being mean and tosses threats at you, like that she'll never see you again, blah, blah, blah. I think she'll need you badly very soon. Don't make them feel like Romeo and Juliet. Just detach. (((Hugs)))