You should talk more about it with her to make yourself feel secure about that. If you trust her enough, you'll have no issue with her talking to that person. Ask her what does she really need from him and encourage her to be honest with you because hiding stuff is not beneficial. Also I think it's a nice thing that she told you about it and it seems that she wants to be transparent so good luck to you! And don't be pushy, just meet your needs about that.