Gee, although I agree that the other administrative professional likely thinks she is doing her job, I think the real kicker where it crosses the line is her including the two bosses. This is absolutely unnecessary for that type of communication and is probably intended to highlight Winter's flaws.

Winter, I will say that if you read the note without tone, there's nothing wrong with what she has written, so you may be reading more into intent behind the email than she intended.

That said, I would personally have called her out on it the first time it happened with a nicely worded reply (perhaps to all, depending on how mischievous I was feeling) along the lines of, "Thank you so much for letting me know about that oversight. In the future, I don't think it is necessary to copy our bosses when it can easily be coordinated between the two of us. They are far too busy to be burdened with such trivial updates. But I appreciate you letting me know about that omission."