I have flown with Maltese, domestic and international.
They must be in a crate under the seat in front of yours. She will be fine, don't worry.
Remember to call and confirm her reservation one or two days before the flight, usually the number of pets in-cabin is very limited. When you get to the airline counter, ask for a pet tag that you will stick on/wrap around the handle of her crate, so all airport employees can easily identify she was "approved" as a passenger.
Don't carry a lot of carry-on luggage, remember you will be carrying her crate through the terminal and will also have to take her out so that the crate can go through x-ray machines.
At Petco (I bought mine there, but I believe many places sell it) they sell a standard in-cabin approved crate that will be ok with any airline. I have never had any issues. It has removable velcro flaps so she can look around and have plenty of air. Keep them open so that she also - and very importantly - can see you at all times.
Offer her water (if you need one, there is a canvas-like impermeable foldable water bowl, at most pet stores) which is very useful imo. Avoid feeding her a few hours before the flight, some dogs are sensitive and might feel sick.
Put an absorbing pad on the bottom of her crate just in case an "accident" happens and take a couple with you.
Let her in and out of the crate for a few minutes a day a few days before the flight, to show her it is ok to be there and she will be out shortly.
My dogs were quite lively but I never asked for the vet to medicate them. I believe I made the right choice for my dogs, but this is your decision.
And don't forget to give her a treat when you get to your destination.