Or maybe not. But here's my experience.
Turns out that i was using auto complete, and my version of her email address didn't match the server. To fix this problem I had to delete all my auto complete emails and also for good measure deleted and downloaded a fresh copy of her contact details from the global directory.
Problem: Reply to All includes myself
Solution: Yell at the sender.
Q: Why am I posting this here? A Blog about food and useless stuff?
A: Because I don't want to sign up to another bloody forum.