Abbey

Abbie is Homer Simpson's English half-sister from "The Regina Monologues".

Appearance
She looks like a female version of Homer (or Homer in drag) and although the two act similarly she is half-British.

Relationship with other family members
It should be noted that while she is obviously a biological Simpson (aside from her appearance and personality, she was born only about a year after Grampa's affair with her mother) she is not officially recognized by the family and never explicitly called a Simpson; the audience is merely left with a strong indication aside from the fact she is still related biologically.

It could be possible that even though she is female, Abbie may carry a Y chromosome, because despite being a woman, she seems to be affected by the Simpson Gene defect that all the men get. As seen in Lisa the Simpson, all the Simpson women have high intellects and good careers because the Simpson gene is on the Y chromosom as Dr. Simpson pointed out

Abbie Abbie Winston Simpson