I'm not sure to follow.
Well in render, when mirroring, you change the orientation of the texture, but not of the sprite object itself.
So the texture's angle could be considered to changed (0->180 as you said), but anyway in events, you don't have control over the texture, but the sprite object. The object by itself on a mirroring isn't changed, its angle still is 0, even if its texture is 180.
I hope you see what I mean, and if I'm not misinterpreting what's happening in C2.
Edit: rexrainbow your last message was written as I was writting this one. This one was an answer to the previous post about a formula.
If you still need clarifications, be sure to ask.
I also hope my previous assertion is correct (Texture =! Sprite object)