Lily is the main character of Ender Lilies and the one the player controls. She has a will of steel, incredible bravery for a little girl and…she’s mute. I’m not sure why she’s mute, she just is.
Unfortunately for her, considering the situation, she can’t fight because she’s too frail. Honestly, understandable, she’s a child. So, in order to survive, spirits - like the Umbral Knight - fight on her behalf. Those spirits also grant her abilities which help her survive and deal with the surrounding situation.
Lily is a white priestess which means she is the daughter of Fretia, the Priestess of the Fount and certified waifu material.
However…it’s later revealed that Lily is, in fact, not Lily…nor is she Fretia’s daughter. In reality, she’s Fretia’s clone. Lily is actually ‘Lily’s’ ‘sister’ (also a clone of Fretia) and the White Priestess who lived in the cathedral. To be clear, all the white priestesses are clones of Fretia. The real Lily was eagerly awaiting the awakening of her new sister…but she died sometime before ‘Lily’ actually woke up, which is sad. That also means the real Lily was the white priestess who interacted with Sigrid.
Anyway, despite learning that she is technically nameless…Lily decides to keep the name, as a way of remembering her sisters. Very nice of her.