It comes from some really sad events where she was once a.Princess of Trystovy but due to some dynastic disputes people sent people to kill her mom and the servanrs she was close with.
They all died trying to protect her and she blames herself for the deaths of her friends and family and she threw away her old name and renamed herself Maggot in a self derogatory way since she believes herself to be a maggot since only survives on eating from the corpses of others including the person she once was
This was also why she trained really hard to get stronger. So that nobody will have to die for her anymore.