They will not refuse entry before verifying different options they have to assess her residence status and the fact that her documentary proof is available with someone in the arrivals hall can only help, it can't hurt her chances.
What's still unknown is whether the card is close to Seattle airport or not. If the card also has to take a flight to reach there then unfortunately i think this question is being asked a little too late. She will have to attend the landing interview without her green card and try to convince them about it.
Do not courier it now, it is too late and it is far better to have it in someone's possession than to have it stuck in transit.