Karen Griffin is Peter's sister, a wrestler who performs under the name of "Heavy Flo."
When she drops in to visit for Thanksgiving in "Peter's Sister". Meg discovers that she treats Peter the same way that he treats her. Although amused at first, she realizes that Karen takes things too far and decides to work with Peter to even the odds. Peter challenges her to a female wrestling match where she is close to beating him, when Meg appears and whacks her with a chair, resulting in a serious injury and coma. While she is in the hospital, Peter rejects helping her by refusing to have his blood type checked.
Karen is voiced by Kate McKinnon.