The "Unnamed Sherri & Terri Lookalike Girl" is a girl who looks like the twins Sherri Mackleberry and Terri Mackleberry. She is one of the unnamed lookalikes of Sherri and Terri who appeared in the show, but this lookalike only appeared sometimes/twice.
She looks almost exactly the same as the twins, but her dress is short-sleeved instead of long-sleeved and the collar doesn't cover up the neck. Her dress also doesn't have a floaty feel at the bottom. Also, she has knee-high socks instead of ankle-high socks. Her face and body are also not the same as the twins.