She is said to visit the Marsh residence once a month, and would visit for nearly a week at a time. On her last visit, she gave her grandniece Shelly a television/CD player/surround-sound home theater. She also gave her grand nephew Stan an evil goldfish that killed numerous people, including Aunt Flo herself and Kenny.
Before her death, Aunt Flo caught Sharon walking into the house, covered in blood and carrying a shovel after burying the first murdered victim of the fish. Flo comments that it reminds her of a time when she saw Sharon doing the exact same thing when Sharon was twelve years old, implying that Sharon may have been involved with another murder at the time. Sharon later buried her in the back yard with the other bodies.
Great-Aunt Flo is an aged and very skinny woman, with vivid red-hair. She has horn-rimmed glasses, a pink sweater, a pale green skirt, grey leggings and black shoes. She is constantly shaking due to the fact that she suffers from Parkinson's disease.
Although she is, for the most part, kind and helpful, she appears to be sensitive and slightly unstable. For example, when she finds out that Stan doesn't like the goldfish she bought for him, she feels that she is a bad aunt and begins to sob. These could be behavioral effects of Parkinson's disease.
Flo is Sharon's aunt. Although Sharon always maintains a pretense of politesse, her visits place great stress on Sharon, turning her into "a total bitch". Sharon always acts supportive of her aunt, often to the detriment of her other family members, onto whom she often vents her frustrations. She does seem to genuinely care about Aunt Flo, as she is distraught after her death. Regardless, she buries her body.
Randy greatly dislikes Aunt Flo's visits, as Sharon acts like a bitch during her stays, often forcing him to sleep on the couch. He acts callous and indifferent after her death.
Due to a lack of meaningful interactions, Flo's relationship with her grand-niece Shelly is difficult to gauge. Shelly received a television/CD player/surround-sound home theater as a gift from Aunt Flo; Shelly thanked her for the gift.
Stan harbors a dislike for Aunt Flo, since her visits turn his mom into a "total bitch". He also received a homicidal gold fish from an alternate dimension from Aunt Flo, which went on to really ruin his day.
- Aunt Flo is a metaphor for a woman's menstrual cycle. This is evident through her name ("Flow"), the fact that she visits once a month for a week at a time and the fact that Sharon becomes a bitch whenever she visits. Her red hair is also likely to be a reference to the blood involved.
- Whenever Aunt Flo visits, Randy is forced to sleep on the couch. This is joke about the menstrual cycle causing woman to become emotionally erratic, often forcing their husband to sleep on the couch after an argument.
- Aunt Flo goes through occasional mood swings (happy to depressed in a split second), much like women do during menstruation. Her actions also affect Sharon, who also goes through mood swings. Stan notes that whenever Flo visits, his mother becomes a bitch.
- The point made about Flo "never visiting again" is referencing the menopause, the point in a woman's life when menstrual periods cease permanently.