Looking for a book I read a long time ago, does this ring a bell for anybody?

I don't remember the title or the author, and I'm having a hard time finding it :( It's about a young girl of unfortunate circumstance who was sent to live with a wealthy family to whom she is somehow a distant relative. She is very meek and kind-hearted, several times a week she crosses a big field to go tend to a sickly poor woman and her children. I can't remember for certain if the main rich guy dies, or if it's just that some doucuments show up with evidence against his right to the fortune he inherited, but it turns out that the girl is the sole true heir to the fortune. That's all I can remember. :(