Sorry I never came back to update! Thank you all for your happy thoughts.
Long story short, we made it to NY and got W officially checked out. It's hand foot mouth disease. Fever almost always precedes the rash, which is exactly what happened to us.
Little miss is on the mend, and she handled it all SO well considering the chaos. We have her on Tylenol and Motrin for the sores in her throat/mouth, which is probably also helping the TOOF popping through at the same time.
What a way to start our vacation! I am so thankful we are with my mom, who took the entire night shift last night so my H and I could sleep. (10 pm - 6 am...we haven't gotten that much sleep since before she was born!!!!!! I am a new woman today!)
Anyway, PIP of our girl on the plane and in the ER. She's such a trooper.

Re: Sorry for the P&R yesterday -- Willa update!
No explanation on the diaper except maybe her pee was more concentrated due the the fever?? (Is that even a thing? My mom suggested that as a reason.)
The weird smell stopped yesterday afternoon as soon as we got here. Phew!
She is ridiculously cute.