Ya, its pretty close to the limit (the dimension is 36 x 20 x 13 inches). What I proposed to my friend is to bring the car seat in box, and if they are very strict, then, take it out, assemble it (takes ~2 minutes), and check it in that way.

It would be nice if she can be sure if she can bring home 2 checked luggage + car seat, or just 1 additional piece of checked luggage.