Mimi's Background

I've watched this movie several times and have always been curious to know more about Mimi, where she came from, who her family was, etc. Nothing is ever said about her family, but I suppose the focus of the movie is on Mimi and Oscar, not where she came from. Has anyone read the book that the movie was based on? If so, were there any details given about Mimi's family, siblings, etc?