If you did it b/c it was the right thing for YOU, then exposing was the right thing. My guess is that many of her family probably already knew (if she's willing to have him at your house, isn't much of a stretch for her to tell one or more of them.
Don't get wrapped up in feeling guilty for telling the truth. Its not your exposing to her family her A that caused problems for her - it's her A that did that.
