I figured it out. If anyone else runs into this issue, and doesn't want to use sine, or platform, or any other behavior in a work around fashion this is how I did it.
Get the plugin rex_moveto -
For Debug purposes I set it up to update a instance variable on my sprite so I could see the angles.
Create Instance Variable - MovingAngle (number)
Add Event - Sprite -> (condition) MoveTo is moving
Action - Set Sprite MovingAngle to Sprite.MoveTo.MovingAngleStart
Add Event - Sprite -> (condition) Compare Instance Variable MovingAngle > 90 AND MovingAngle < 270
Action - Set Mirrored
Add Event - Sprite -> (condition) Compare Instance Variable MovingAngle > 270 OR MovingAngle < 90
Action - Not Mirrored