Can an at-will employer fire an employee for missing work due to an acute, non-ongoing, medical issue?

Question Details:

A friend of mine was let go when she missed a week of work for a respeiratory issue after she cleaned her carpets. It's a treatable condition requiring oxygen and steriods for a couple of weeks. She will recover and be able to return to work. She is a contract worker in Washington State. Where does she stand in regard to her termination? Important Notice