She is Michelle Tanner's best friend.
Denise Frazer is one of Michelle's best friends, played by Jurnee Smollett.She would eventually be the one who replaces Teddy after he moves to Texas. She first appeared briefly in the episode Girls Will Be Boys, and again in The Long Goodbye, after being transferred into Michelle's class. This was when she became a regular character. Denise, like Teddy before her, becomes Michelle's "partner in crime", and accompanies Michelle whenever she has an idea. In the episode Be Your Own Best Friend in Season 7, Teddy moves back to San Francisco, leaving Michelle to choose between him and Denise for whom to portray as her best friend. At the end of the episode, Danny makes her understand that it is possible to have more than one best friend. Michelle, Teddy, and Denise all become each other's best friends.
In the episode Too Little Richard Too Late, Denise reveals that Little Richard is her uncle. When he comes to the Tanners' house to pick her up, Joey convinces him to perform at his campaign rally to be elected President of the Frasier Street Elementary School PTA.