A 12 year old should be looking at a B2.
Let her parents apply for the visa and yes you will need their permission for you to travel with her without them.
Get married in Mexico?
Visiting the other half can cause issues when applying for a visa, hopefully she did disclose you.
She can always apply for a new visa.
Translation he submitted a fake divorce certificate, now the Consulate check these things, after all if I have come across this numerous times, you can imagine how many times the Consulate have seen it?