Legal Question in Family Law in New Mexico

This sounds more like a problem for Dear Abby than a legal one. From that perspective I would suggest you discuss it with your intended and put off getting married and putting your daughter into living quarters where she may not be able to avoid contact with the 6 year old until you get this sorted out through professional counselling.

From a legal perspective, Grandma could be subject to child abuse or neglect charges. The correct thing to do legally in this circumstance is to notify the Children Youth and Families Department (CYFD) that the 6 year old may be subject to child abuse. CYFD is a mixed bag, from my experience and reports from others their response could be anything from sheer boredom to sheer panic. Nevertheless the law requires you to report this and requires them to investigate it. Your intended should be prepared to fight with CYFD for custody.

Still discussing the legalities, the problem is very complex because of the complexities of the chirldren's code and the criminal sexual contact of a minor statute (30-9-13).

Generally age 14 is where the offenses committed by children transition from the less serious sanctions applied to delinquents to the more serious sanctions associated being a youthful offender or serious youthful offender. The 13 year old is probably subject to juvenile criminal intervention, and technically so would be the 6 year old, but it's not clear to me how the Children's court would deal with the 6 year old. The 13 year old could be in trouble. You can contact the Children's Court Attorney in your area to initiate court action.