My son was 7 1/2 months old the first time we flew.
#1 Bring a snugglie, or some carrier to go through the airport with.
#2 Bring an extra shirt for you and outfit for your little one in case your little one spits up on you or themself.
#3 If your child has a pacifer you can use it for take off and landing.
#4 Check with the airlines, but you should be able to bring food for your little one. Not sure about how to heat anything up, but the airline might know.
#5 Bring a stroller, you can feed in the stroller in the airport. And you can gate check it, so you can go through the air port with it.
#6. You can bring milk/formula through security for you little one. They did not question us about the amount. I was nursing so I brought several bottles with so we would have a small stock at our destination.
#7 Bring toys with for your little one to play with. That will help occupy the time.
It sounds like you did not purchase her a seat, but you might be able to request an extra seat that is available on the plane for your little one. If there is an extra seat you can put your little one in the car seat and they will offer you a place for the little one to eat.
You can also talk to the air lines to see if they can offer you help with the little one. I am sure you are not the first one to take a little one alone on a plane.
Good luck