An uneducated grandmother who does not have children living with her but pays for public school education through her property tax is a:

Forced Rider

Explanation:

A forced rider is a person in the society who is made to pay taxes or dues for services that he has no interest in or even benefits from. The forced rider might even have personal convictions against the product or service, but he is still made to share in the cost of the government providing the service. For example, advocates of climate reclamation might be made to pay for services like the maintenance of industries that pollute the environment.

In the case above, the grandmother has never seen the four walls of a school, nor does she have school children whom she cares for, but she is still expected to pay for public school education through her tax. She is, therefore, a forced rider.

i believe the answer would have to be a dependable person