I've always wanted my mc in my wip to start out as a normal happy girl with a loving family and good friends etc...and then during the course of the novel things get dark and her once happy world is gone.

So, my question is, how do I do this without making her appear like a sissy mary jane type? I know how important the beginning of a novel is. Should I perhaps start with something dark than reflect back on her happy life. Or is it ok to start out with her being happy?