It is virtually never claimed that Nichelle Nichols was the first African American woman as a member of the regular cast of a television series. Cicely Tyson, for example, on East Side/West Side, offers a significantly earlier example of that.

Nichelle Nichols is conventionally identified as being a participant in the first interracial kiss on a scripted TV drama on American TV, in Plato's Stepchildren, November, 1968.

She is of course likewise described as important for having been an African-American woman in a non-stereotypical role, but this latter is a rather subjective characterisation. It's rather difficult to nail down what might have been the first "non-stereotypical role" for an African American woman with any confidence.