Shirley is the Loud kids' paternal aunt, who first appears in the episode "Picture Perfect".
Very little information is known about Shirley, other than she is either Lynn Sr.'s or Rita's sister/sister-in-law.
She first makes a brief cameo in "Picture Perfect", where Luna compares Lincoln's homemade coffee mug to her, in the sense that both look ugly.
Shirley is a very repulsive woman, with fair skin, curly red hair, and a freckle on her left cheek. She wears an olive toned dress with light green spots, three golden bracelets on her right arm, round olive earrings, and pink lipstick.