She is a mystery.
Much isn`t known of her.
She was found buried alive in Dranacs cemetery, mangled, from where she was rescued by Shadoweyes. Eyes placed her in front of a hospital, so she could be helped.
For some reason she, apparently, didn`t get any. Instead, she kidnapped Sparkle Park.
They were found by Shadoweyes. Eyes and Mummy girl fought against eachother. Shadoweyes could`ve killed her. But she couldn`t. The girl escaped.
When she returned the next time, she was about to do something to Sparkle (probably attack her). In the upcoming book, Shadoweyes unmasked, it will be found out what it is.
Mummy girl is mute (either since birth, or trauma ). She`s also mentally unstable (Most likely due to the fact that...well...she was buried alive. It`s not certain though.), and is, it seems, obsessed with Shadoweyes.