planes cannot be mirrored #1.
Plane PropertyManagerYou select geometry and apply constraints to the geometry to define reference planes.
Follow the messages to create a plane and see the plane status. The Message box color, plane color, and PropertyManager messages help guide your selections. The plane status must be Fully defined to create the plane.
you can copy and paste the sketch on the new plane, then use the sketch modify tool from the tools pull down:
Sketch Tools > Modify Sketch or look at the help file under