I took control.
Interesting idea. As other have said : the game is pretty unintuitive, but I don't think an hint system would have been the ideal solution. Making the mirror actually reflect the world around it would immediatly hint to the player that something must be done with the reflexion. Personally, I was convinced that it was just a plate of glass before placing it next to the button.
Solid effort though, I'm sure you just need more practice to give your ideas the mechanics they deserve. After solving the first puzzle the second and third just goes without saying. Nice work.