Are you wee wee pad training? Our Toto is 2 1/2 years and we regularly fly from Grand Junction, CO to Birmingham, AL with her. We try to get the least number of stops and shortest flight times. I don't know about one that small but it's been our experience, because of delays, missed connections, etc., you need to absolutely be prepared. I take more stuff in my carryon for Toto than for myself! Bottled water, little water bowl [we offer her water every chance we get], treats, wee wee pads, extra blankies, extra shirt/sweater, toys and at least 1-2 servings of her food. We have had cancelled flights and had to stay over for next day flights and every other delay you can imagine! We have had great flights with absolutely no problems and had nightmares too exhausting to describe! As long as I have everything I need to make sure that Toto is comfy and prepared for emergencies in her carrier .... she usually does better than we do!!
I always fold a wee wee pad and put it under her little blankie inside her carrier just in case she absolutely cannot "hold it". If she does have an accident [and it's rare but can happen] all I have to do is change her pad & blankie, clean her up with wipies and change her shirt! Be sure to take a few large & small ziploc bags to store pee pee blankies/shirts in so your carryon doesn't smell like pee!!
Didn't mean for this to be so long but there are so many things that can happen and I hate to see anyone as shocked/surprised as I have been! Oh, and angry .... did I mention angry??
Bottom line, you will meet lots of great employees of most of the airlines ... but truth be told, there are some who could care less and just treat you like they think "you shoulda left that dog at home!!" It's pure luck when you have an attendant who will actually let you take the baby out of the carrier on the plane ... most will not but will maybe let you hold the carrier on your lap except takeoff/landing which comforts some if they are upset. We always ask first ... it's almost as though they do not like their authority challenged but if you ask, they will usually say yes ... they're still in charge of the decision! Toto understands that she cannot get out and seems to find comfort in a hand slipped in her carrier that she can lick & snuggle!!
Good luck!