Let's start with the fact that you have a curtain in front of the window in this case, the question of the alpha Beck behind it is no longer relevant. Only then do Plaine with a picture of the window.
With regard to the alpha mirror, it is in principle possible. You have to do everything as described in the topic of alpha-channel , not only disables revlekshen in the global settings, and the window make luminous Plain or himself back. Then the glowing back simply be reflected in the mirror and you will be able to allocate it to the color in Photoshop the same Magic Wand. But in any case, substitute back in Photoshop on the reflection in the mirror - a bad idea, though, because you need to reflect, scale and shift the image in the mirror so that it corresponded exactly to the picture outside the window. Simply adjust the picture to beke all.