I need to register my niece in school,both of her parents are in jail and her grandmother my sister does not have room for her at this time, what do I need to do? School starts next Monday in our county.

It is an admirable thing you are doing to take on an additional child. Bless you for that.

Have you called the school and told them the circumstances?
They may have all the answers to be able to let you know what you need to do.

Try this first if you haven't already.