How can I prepare my dog for a 3 & 2 hour plane ride?

Your plan for exposing her to the carrier is a good one. Don't feed her before the flight - maybe just a biscuit. Let her have water up until you leave for the airport, and offer her water between flights but don't be surprised if she refuses. If she DOES drink, limit her to a couple of ounces so she doesn't load her bladder. She's going to be frightened by the strange noises and smells so don't rely on her behavior being normal. Make sure to keep the leash attached to her collar so she can't bolt if she panics when you take her out of the carrier between flights. Hopefully you will be able to get her outside for a potty break between flights but she may be too upset to relieve herself. Put newspaper in the bottom of the carrier in case she pees because of fear. Do not put a blanket over the carrier. She needs air. Airline policies vary, and some flight attendants adhere to them more strictly than others. If the flight isn't packed, and your seatmates are family members, ask if it would be okay to have the carrier in your lap for a little while once the flight is underway. They may say okay, but keep it closed, or may let you open it to pet her as long as she stays in it, or they may let her out to sit on your lap for a while. They may make a big fuss over her and offer her treats. Don't forget that your fellow passengers may be allergic to, or dislike or fear dogs. You and the crew need to be sensitive to their rights too.