Oh, time for my Peer Mediation skills
Listen, you did nothing wrong because even if you had told him the secret, he would've said "I know already". Girls (No offence) get all crazy about a guy and all they do is talk about him. I have two friends which are girls and they are exactly like that. One of them likes a guy and he doesn't even know she exists and the other stalked the guy for a year and now they're finally together. Oi. And if I said something bad about the guys, I would get flamed big time. Therefore she is flaming you because you might've "ruined" her chances to be with him even though she knows he knew before hand.
Trust me, if she is still mad at you than she isn't a good friend. If she wants to go and see if she has a chance with him, let her do it on her own. She doesn't deserve you as a friend.