A "latch-key kid" is someone whose parents are so busy that the kid is alone most of the time and they have their own key to the house.

Not gonna lie, this definitely explains a few things.

Yup, ignored by her parents, losing her one friend, it does explain a lot.

Also her line about recreating 'Our old house', perhaps she spent so much time at Sunburst's place rather then her own, she saw that as her home rather then her real one?