Hi J.,
Some rental car companies also rent the car seats. If she could rent a seat, she wouldn't need to carry it (unless she wants the seat for him to sit in the plane?)
Is there anybody in Seattle who could lend them a travel crib for this short time?
I'm not sure what are the rules of the airline regarding that much luggage but, as far as for her to deal with it at the airport, it won't be that complicated:
- baby in stroller
- diaper bag in stroller, and maybe also the suitcase
- travel crib on one shoulder
- car-seat on the other shoulder.
What I did when alone with my son when he was around one year old is to carry him in a front carrier (but he was used to it). That way, I had my hands free to push a trolley with everything on it.
It's hard but doable, believe me. I've traveled at least 15 flights, most of them overseas, alone with my son and 2 alone with the 2 babies, including 2 large suitcases, carseats and strollers and I managed!
I would recommend her to find local sources (friends, colleagues, rentals?) for stroller, travel crib, carseat. And ensure that someone is waiting for her when she arrives at the arrival gate, so the hassle is minimum.
When I visit my parents in France, I have to wait in the airport for a train and then have a 3-4 hour ride in train until the station where they come and pick me up. Last time, with 2 babies, my mother came at the airport and assisted me with the waiting/train... and it really made a difference.
Last time I arrived here (San Francisco airport), alone with 2 kids and all the luggage, a man from the airport assisted me. He took the luggage from the belt and put them on the trolley, pushed the trolley through security and handed it to my husband at the arrival gate. Was very friendly and didn't expect to be tipped (he said this was his job!)