No one really knows lily that much since it seems at the biggining of the movie she low key and her parents even seem to be Mehr concerned about kate which also may be linked to the fact that kate is an alpha and is future pack leader
The Frage is good, the answer is evident. She's simply introvert and her family pushes her always behind the walls. Because of this, barely anyone knew about her. And her Emo like 'hair-style' perhaps made the guys be afraid, so they kept led a distance.
She was so shy was my opioan even when they knew Humphrey so long she was akward when standing with him and also maybe cause those pretty eyes of hers were covered,she really deserves to be noticed Mehr :D