Do it near the end of the flight because if she says "no", it will not be a good flight.
Do it privately. No need to get others involved.
After she says "yes", you may tell the flight attendant and maybe a glass of wine will be served. If you want a video, ask a nearby passenger if they will take a video. You may give them a note. "I am about to propose marriage. Are you willing to make a video. If yes, come with me and I will show you how to use my phone." Maybe also translate in Dutch, too. Or ask a flight attendant to do it.