Are "Nana" and "my mother" the same person, or are you talking about two different grandmothers (e.g., "Nana" is the mother of your child's other parent)?
And this was how long ago?
Is there any particular reason you didn't walk next door and tell your daughter to get her butt home?
If you're talking about NRS 200.359, it only applies to parents of the child or persons who have "a limited right of custody to a child by operation of law or pursuant to an order, judgment or decree of any court." I assume "Nana" is not your child's other parent, and you did not mention "Nana" having any right to custody. I disagree that the definition of "conceals" is clear, but that's a moot point. What you're describing could, theoretically, be kidnapping.
I'm sure you can do a great many things, including exactly what the police told you to do: wait until the court date to see what the judge says about the guardianship. It's baffling to me that you didn't take any action the day after your daughter spent the night when she didn't return home. Given that you waited to contact the police until "Nana" filed a guardianship petition, the refusal of the police to take any action makes perfect sense. If you haven't already consulted with a local attorney, you would be well-advised to do so.
P.S. Has your child started school or will she soon be starting? Any reason you can't pick her up after school and bring her home?

