What if she was impregnated by her 12 or 13 year-old husband-to-be? Would it be that bad then?
Didn't men in their twenties used to take 13 year old brides all the time way back in the day(pre-1900's, even early 20th century)? I'm pretty sure they did. And this is from a native tribe somewhere in Colombia... To them it's probably common practice to be doing these sorts of things. And it has been for centuries.
I'm not saying it's right, but just being a bit of a devil's advocate.