Hi, ex flight attendant here. Hope this helps.
honestly, my biggest advice is to not worry about other people being stressed out (easier said than done, I know). I could write a book with stories of annoying behaviours on planes but an upset/bored/distressed baby or toddler is not one of them. Kids make noise and it’s just part of life. You’ll probably find that most other passengers sympathise and will have been in the same position with their children! Anyone who judges an upset child or parent isn’t worth stressing about😊 You’ll hopefully find the crew will chat away to her and be extra nice as they will understand how stressful flying with a young child is.
Having said that, obviously don’t let her run wild during the flight (I’m not saying you would but plenty of parents do unfortunately!). Don’t walk up and down with her in the aisles when food services are being carried out (risk of hot food or drinks spilling) but in between services when the seatbelt sign is off, there’s no problem with parents taking kids for a walk up and down the plane! Bring lots of colouring books, pencils, toys, games, picture books, ipad, movies, basically anything that will entertain her. Avoid things with small parts like jigsaws or board games as if there’s turbulence and it’s knocked over you’ll struggle to find all the parts between the seats and the floor and she might be upset by this. Don’t bring anything glittery as it is an absolute nightmare to clean afterwords and bring a plastic bag for any rubbish too. Don’t stick anything to windows or seats unless you can be absolutely certain you can get it off and you will do this before leaving.
Bring a favourite soft toy and blanket as flights can get cold and the plane blankets are usually rubbish! Maybe get her one of those teddies with passports and a suitcase so that it’s going on her holidays just like she is. Some parents would play little games (things like drawing the clouds and what animals they look like) but I think most parents just opt for iPads and snacks to keep kids entertained on flights. The child’s happy and the parents can relax a bit too- everyone’s a winner! Bring a portable charger in case it’s needed.
Also, make sure you eat before going on the plane and try to get a good sleep in the days leading up to it (easier said than done I know!). You’ll be so focussed on her during the flight that you’ll barely eat or sleep yourself so try to make sure you’ve got lots of energy before going on to get you through the flight.
with regards to changing on seats or laps, do NOT do this. It doesn’t matter if it’s a wet or a dirty nappy, it’s disgusting and extremely unhygienic. Parents do this ALL the time- honestly, there’s a reason flight attendants will never open a tray table when flying as a passenger- we know how often it’s used as a baby changing table and it’s absolutely disgusting. Use the toilets, I know they’re small and not ideal but that’s not an excuse to change a child on a food table or a seat.
hope some of this post helps you. Have a great holiday!