I did a ton of searches on here and it seemed like everyone was recommending the car seat or harness. I think she's more likely to sit still in her seat, but I'd love to avoid lugging it around if we can.
For a 3 year old, it's more of a personality thing. For 2-and-unders, when being a lap baby is possible, then it's "bring the carseat and use it on the plane", because kids that little often have a problem staying in a lapbelt, and having their own seat is much safer in case of extreme turbulence than being held by a parent. But after that...personality.
I brought the carseat until DS was nearing 4, and then one trip our flight was canceled and we were put on the next flight leaving, oh, NOW, and the thought of lugging the seat down to available seats (it was on SW) keeping it over the heads of passengers on a nearly full plane just made me want to cry. So I gate checked it right then, DS was totally fine, and that was the end of that. But he was a seasoned flyer by then.
One thing to be sure of... Have at least one thing that isn't electronic so she can have something for take off and landing (the actual take off and landing will probably be cool enough to entertain her, but the taxing part is kind of boring)
YES. And don't bring the electronics out until the electronics can be on! That recent thing in the news (3 year old wouldn't sit in seat, family had to take a different flight), IMO, could have been partially avoided by not bringing out the electronics while sitting on the tarmac.
Bring a nice little book, or coloring book, or something low-tech and simple for the times when you can't use electronics. Also let her know many many times that at some point during the flight the electronics will have to be turned off, and give her warning of that! I would estimate half an hour after takeoff and before landing, you're going to need the low tech stuff, so make sure those expectations are set!
Don't be the first on board, that makes you sit for an extar 20 min or so confined in the small space.
Yes, I totally agree!