Lil and her brother Phil are adorable twins who are alike in almost every way possible. Usually dressed to match, they both wear pink with black-pinstripe shirts and turquoise outfits (Phil's being a shirt and Lil's being a dress) with a handkerchief on the left side and a duck on the right, and both had a small amount of brown hair on top of their oddly-shaped heads. Lil wore pink shoes, white socks, a pink bow on her hair and no shorts (exposing her diaper like Tommy Pickles), and was always drawn with ear lobes. Lil is older than Phil by two minutes. They also shared the same interest: consuming worms (which they have often called "Chocolate Spaghetti") and toilet water. They often used their "full" names, Phillip and Lillian, against one another when arguing. Their parents, Betty and Howard, often confused the two despite permanent differences, like the ears, as well as (of course) their genders. It is often believed in various fan circles that the inspiration for their names may have come from Ayn Rand's book Atlas Shrugged, which features two in-law characters named Phillip Hardride and Lillian Rearden.
In All Grown Up! Lil has turned into a independent and tomboyishly beautiful pre-teen. She now has her own group of friends and thinks bugs are gross. She isn't fond of many things that Phil and her used to do and now has developed her own style. Despite her beauty, she sometimes acts more mature than Phil since she is 2 minutes older. She loves speaking her mind and standing up for her friends. She even sometimes hangs out with Angelica and gives her advice! Although she does have some things alike from a brother. They both like soccer and are on the same soccer team. They can also be very competitive and jealous against one another. However, they both shown to love each other dearly and still enjoy wrestling around on occasion.