A lot here and I really hope it helped you to write it out here!! (And travel is a lot not a little stressful with kids and you took on the sister situation!!). I hope it's better with her away -I think you had a lot of trouble restraining yourself because of the small space, you were tired, your baby wasn't feeling well,,,,,, and on and on and on. You are human. And it doesn't sound like your sister is second mom when you travel -the doting aunt who anticipates what you might need as a mother of three little ones. She's not going to come over, say hi and look at you and say "K I got this - you go shower, take your time, make yourself a cup of tea -I'll handle the kids --- ok go now!!"
Anyway I really hope it helped to write it here and I'm glad your husband drove her back.