I am trying to decide on a carrier so I can fly with my little pug. She is about 17 lbs and will fit into a medium sherpa carrier, though the large gives her more space to move. I would prefer to use the large, but I'm curious if anyone has flown their pug on Southwest. Since they are new to animals, I'm worried that they will deny her carrier if it doesn't exactly meet the underseat specs. Thanks for any feedback!