Given Lisa’s appearance and attire, I can help but postulate the possibility that one of the Loud parents is a descendant of Shaggy Rogers and Velma Dinkley.
Perhaps Lisa is their granddaughter, or great-granddaughter? The color scheme of Lisa’s attire is pretty close to the color scheme frequently worn by Shaggy Rogers, yet Lisa also has brown hair and wears a turtleneck much like Velma Dinkley.
A silly theory, sure, but I find it to be an amusing idea :)