I'd rather not use the is mirrored and set an instance variable for the direction the player is facing, but yeah, that sounds about right..
The if not mirrored should be a sub-event so the else event would only react to the "if not mirrored" condition.
Else doesn't need another condition attached, just right click and select add "else"
to be honest I really don't know I never even thought about that good question.