This part of the plan for my fic that expains her background.
Summer's sister died when she was eight. When she found Elizabeth dead she did not know that her neighbour, an unregistered animagus, was the murderer and thought it was her 10 year old brother Spencer, because he was standing next to the body. She attempted to use the killing curse – Avada Kedavra – on him. The spell missed. As the curse is an unforgivable curse, and the evidence of the dead body she was convicted for a life time in Azkaban. Her cell wasn't heavily guarded. She learned the patronus charm which she performed with the broken wand of her mother.
The summer after second year she went to visit Harry multiple times but didn't mention anything related to magic to the Dursleys until the Quidditch World Cup a year later. Dudley not knowing she was a witch had formed a tiny crush on her.
Pre-Hogwarts she had a very close relationship with Draco Malfoy. Even when her friends think he is evil, she sees past that and into the good at the bottom of his soul. Draco also gave her a green serpent ring for her sixth birthday.