It's a great thing to have a friend who is there for you, even knowing about something like SI. You didn't do the wrong thing by telling her you lied to her, that was a good thing, if you hadn't it would have just eaten away at you. I agree with Sweet Crusader, you need to explain to her why you lied, and how you feel.

Hopefully everything will work out. Let us know how you are doing, and what happens.