How to turn a window into a mirror?

Hi Jennifer, purchasing "mirror" cut to that size would be very expensive. They do make mirror spray paints that I've been pretty impressed by. Its not a perfect mirror finish but it looks pretty neat. Spray painting the backside of the window will make it look more authentically like a mirror.

Jennifer....Depends on the window but you might be able to remove panes and find a mirror the correct size to add to the back. You will need to maybe add screws with a small metal plate that will hold mirror in.

https://www.hometalk.com/diy/decorate/mirror/turn-glass-into-mirrors-29461033

https://www.hometalk.com/diy/decorate/rooms/diy-turn-glass-into-mirror-28277760

https://www.hometalk.com/diy/decorate/mirror/how-to-make-a-mirror-with-mirror-paint-5719847

Could you paint it with mirror paint?

Here is an idea for a repurposed window mirror https://www.pinterest.com/pin/633178028840937108/

Hi Jennifer, hope this helps you out,

https://www.youtube.com/watch?v=Ub_ZbxG6thw