I agree with everything Karlin said about Abbey and considerations for flying. I know that it's hard to think about leaving her when her symptoms are not quite under control, especially since your son will not be home during the day to monitor her. Is there anyone who does day care or boarding in their house? I have a friend who is an ex-ER nurse who started a doggie home care business. When I go out of town, my dogs go there (she is home all day with them). Since she is a nurse, she is very acute at picking up on medical issues.
But, generally speaking, I have flown numerous times with Riley, my SM dog who had surgery in June, 2008. She has been a dream and shows no ill effects from the air pressure changes. She is so quiet in her little bag, no one even kows she's there until we get off the plane and I open up the top of her bag. If I know I am upgraded to first or business class, I take a large Sherpa carrier. It doesn't quite fit under the seat, but the only thing it does is limit my leg room. I always request a window seat - the under seat configuration is larger on American Airlines in the window seat. If I am flying in coach, I take the medium Sherpa. She's not quite as comfortable in that, but it does fit under the seat better and she's not UN-comfortable, just less room to move around in. In my experiences, the ticket agents don't care how big the carrier is, they look to see if the dog has enough room to move in it and to see how cute your dog is! I checked out the cases with wheels but didn't like them because the wheels took up valuable doggie space. Riley does get heavy carrying the bag on my shoulder though, especially if it's a long walk. And Riley is little - she only weighs 12 pounds 1 ounce. After we go through security, I carry her in my arms to the gate and have never had anyone complain to me or ask me to put her in her bag. When we get off the plane, I usually leave her in the bag, but let her put her head out so she can see where we're going. I always have to check a bag when I travel with her so I take her outside immediately when we get off the plane for a pee and/or poop and then go back in for luggage. She is always in my arms then since she gets overwhelmed if she's on a leash. But she is a great traveler. The longest flight she has been on is from Chicago to Arizona - so she's on the plane for about 4 hours. I have never done a flight with a connection yet, although I did have one time that we had to change planes before we even took off. I raced her outside to pee one more time and made it back in time - quite a feat since I had to go through security again.
Jsut to recap, no bad experiences flying with an SM dog who is managed with meds and is not in pain and is a very quiet, calm dog.