Now that I've thought about it, I honestly have no idea about her childhood except for the fact that what inspired her to do magic was a fireworks display and that she was with Rinnosuke during that time.
Although, going by her current personality and state of affairs right now, I don't think she had that much of a good childhood. I don't think she had many friends, I don't think she was brave during that time and I don't think her parents let her that much freedom. So she came of age, she pursued what she wanted and just left her father's house to live alone and do what she wanted to do.
And honestly, if I was with her during that time, I guess both our lives might have turned out differently and not in the expected ways.