Well, I did the confrontation. Told her I knew that she had lied, had tried to manage things behind my back. I have no idea why so many people feel that a dignified silence is best. Why one persons feeling are so much more important than anothers. I don't go in for a row, just a statement of fact...
In my case she sort of squared up a little, so, before she could speak, I added a pre-prepared sentence "Don't bother. You will only lie again to try and cover your embarrassment" and walked off.
People who were with her reported that she had sky rocketed, really, really lost her temper. But she never acknowledged she was in the wrong and people who liked her continued to do so.
If you do do it, practice a little, not too much, maybe just the most important sentence. And then leave them to it. You won't get what you want, so accept that you have said what you wanted to say and that both they and you know precisely what they did.
Good luck, have fun with it, even if you don't ever speak to her directly.