RN refusing MA assignment

I am a nurse practitioner/back office manager in an OB/GYN office. A few weeks ago, we had to let go my medical assistant so we are work short handed until a replacement is found. She was also the "float" in the office. One of the other MA's this past week was off on vacation as she was getting married. THEN, another was out because her son was admitted emergently to the hospital. That left us with 2 for 4 physician's. The good thing is that usually there is one physician off per day and I can handle my own patients. SO-We had asked our triage RN to fill in and help be an MA for the day. She refused, initially, stating that it was against her licensure to be an MA (and go downward?) The position includes getting weights, blood pressures, stand by assist if needed. Clean the rooms. I have even filled in when the situation has arisen. I don't ask anyone to do anything that I, myself, am not willing to do. This particular day, I was to do my job, my MA's job, and by the phone triage person as well. She was angry because she also stated that such duties were not in her job description, however, the "clause" is performs other duties as necessary, especially in effort to assist, learn from and take direction from managers. Also included in the job description is clinical duties which are not performed by this nurse which now she states she is unable to perform because she has "now not been a clinical nurse for 35 years." "I was hired to be a triage nurse and a triage nurse only." She called in sick on Friday. This woman will be asked to fill in only one day this next week, as the MA that got married will be returning and the one with the ill child will still be out for another week. Any thoughts? Am I out of line in my expectations?