Hi Monica,
I've just been having a look for you as I was intrigued by your question! I have come across this post on Houzz which might help you out, scroll down to the comments and there is a picture in there which might suit you as it has a mirror which is fitted in front of the window as it fastens to a bracket on the wall rather than the mirror being attached to the wall itself.
[https://www.houzz.com/magazine/a-window-above-the-bathroom-sink-feature-or-flaw-stsetivw-vs~1196083[(https://www.houzz.com/magazine/a-window-above-the-bathroom-sink-feature-or-flaw-stsetivw-vs~1196083)
Otherwise how about something like this maybe?
Hope this helps, would love to see some images of what you decide.
Q
