Throw her in jail for Illegal possesion of a firearm. /sarcasm
Supposing she is a citizen of New Mexico, regardless of age, the following should apply to her:
NM Constitution
Art II, Sec. 6. [Right to bear arms.]
No law shall abridge the right of the citizen
to keep and bear arms for security and
defense, for lawful hunting and recreational
use and for other lawful purposes, but nothing
herein shall be held to permit the carrying
of concealed weapons. No municipality
or county shall regulate, in any way, an incident
of the right to keep and bear arms.
You know, I wouldn’t be surprised if the Lib’s didn’t critize the mother for not having the rifle locked up so the girl couldn’t get to it.