What is Precocious puberty a doctor says your 8 yr old granddaughter has this is this a bad symptom?

8 isn't that young, but it is early to have a period or pubic hair, but breast development isn't unheard of at that age.

It simply means that she's hit puberty extra early. This isn't necessarily a bad thing; however, good nutrition is especially key at this point in her life, as her body is trying to continue to reach its full growth at the same time there are changes going on from puberty.