Legal Question in Family Law in Missouri

You might want to consider filing in Probate Court in the county where you live for guardianship and maybe conservatorship of your niece.

Barbara is correct. But, if the child;s father consents, you can get letter fo temporary custody from the mother (also signe dby the father) that might suffice to be able to enroll the child in school in your district.

Good luck

The previous responses are correct, but I wonder if you might try having the mother (and father) sign a Power of Attorney naming you the attorney in fact for the purpose of taking care of the child. The statute requires such a power of attorney to be renewed annually or it expires, but at least this would give you some protection while it is in place. No matter what you elect to do, good luck!