Hi
You can only rotate the image by entering the angle required under the Motion effect. (180 to invert it) Flip right or left is not possible unles you use a plugin.
There is a plugin called "Flip horizontally" but it is an internal filter used by virtualdub. I am not sure whether it is available as a .vdf file that can be incorparated into VP.
The Free Studio 2013 download that Borate mentions works OK and will flip left-right or top to bottom with no problem.
Nat