I'm impressed that anyone has been able to do it!
As a mom of three, I can attest that the first few weeks, you are exhausted, getting used to a new baby, off a sleep schedule, feel like hell, and are overwhelmed emotionally all while being amazed how beautiful this new little creature is! I can't even imagine packing for a vacation, much less traveling and staying somewhere overnight. It wasn't uncommon for my kids to go through 3 outfits a day between spit up and violent runny poops (sorry for the graphic description). How do you do laundry on the road?
I would encourage her to stay home. In fact, encourage is the polite way to put it. Realistically, she is going to be stuck in a hotel room since its so hot in Sept. and newborns can't regulate temperature well. (pools are *definitely* not an option either).
Anyway, good luck! Help her make a wise decision... But also let us know that it was wonderful and we were all wrong!