My friend completely lied!?

I'm changing all names except mine (Emma).

So my friend Anne has never been the best friend. She always acts super silly, and you surely can't trust her with secrets. So, one say my freind Sally comes up to me in Choir class and says "Really? I can't believe you would tell her things like that?!" And storms away. I was completely confused: I really had no idea what I had done. So, I go up to her and say,"I really don't know what I told anyone. You haven't even told me any secrets that recently that I would WANT to tell anyone." She said "you should know.." And walked away again.

So, that afternoon on the bus, (SALLY AND I ALWAYS SIT WITH EACH OTHER), I had saved a seat for Sally, but she ignored me and kept walking. So I say by myself.

That evening, I texted Sally and said "Hey, I really don't know what I did."

Sally then said "You told Anne something. A lie."

I thought for a while, then had no clue, so I told Sally "Can you just tell me what I did? I'm really sorry".

She replied "YOU TOLD ANNE THAT I LIKE JOE, and that I'm obsessed with him, talk about him all the time, and even write notes to him!"

I had NEVER EVER done that. Sally had likes Joe in like, 3rd grade, but were in 7th grade, and since Sally and I are very close freinds, I knew she didn't like him.

So I told Sally that, in person the next day, and she believed me. So, we both found out that Anne lied. I'm torn on how mad I should be at Anne, or how I should handle this. Advice? What would you do?