Most people who are against child marriage are against all forms of pedophilia. So I sort of see why you did what you did there. But I'm personally against child marriage, more or less, for various reasons.
But child marriage may be the best alternative to get antis to accept some forms of pedophilia. After all, pedophilic child marriages are sanctioned by virtually every religion on the planet. So it's somewhat possible, even likely, that one day antis could be convinced to agree to it. But I still don't think it's ideal. It would likely single out boy lovers as well.
I just don't know why you'd see child marriage as so important to message her to convince her of it, unless you were trying to promote pedophilia in general. Child marrriage seems like an awfully big decision to expect a girl to make, especially since they are usually forced into it. It's a decision that's supposed to last a lifetime. I don't think that's fair to a child.
I'm somewhat inclined to agree with you though. I mean, not only are most people against child marriage against everything MAP-related, they also are likely to be feminists! They believe in bombing countries like Afghanistan just so that girls won't be married off, and can go to school. Meanwhile, they turn a blind eye to Afghan men raping little boys. 'Bucha Bazi'. Even the Amerikkkan troops turn a blind eye to that.
The horrors of feminism, misandry, etc, could not be more evident in how they run rampant in our world today, destroying the foundations of the only humanity we have left!