Is a doctor’s note enough to prevent us from firing employee who broke call-in rule?

Q. An employee left work on a Monday due to an illness. She called in sick Tuesday and Wednesday, but we heard nothing on Thursday or Friday. Our policy calls for termination if the employee doesn’t contact us within three days. We posted her job on Friday and decided to terminate her. On Monday, her fiancé called to tell us she was pregnant and had complications that led to a hospital visit. We got a note from her obstetrician saying she’d been examined, but not indicating when she could return. What should we do to avoid any legal fallout?