So it happened that I asked a person to take a picture of me with Huawei P9 Lite smartphone. She said she took it but it happens she didn't because she didn't even press the button. I know this sounds crazy but is there any way to see that photo she had to take? I mean the camera was turned to me and the camera app was opened.
If the picture was not actually taken, you cannot recover it. Your phone doesn't record what's done on the camera screen, unless you actually record a video or take a picture.
If it would be recording the whole time, that would take all your phone's memory and it would probably be against some privacy laws.
The above is assuming that you didn't download a special camera app that has this function.