Dr. Sandi Zober was a doctor who worked at Mercy Hospital
Dr. Sandi Zober was a medical professional associated with Mercy Hospital
I prefer my original version, which above appears second.
"Medical professional" avoids the redundancy of "Dr. Sandi Zober was a doctor."
We have no way of knowing that she worked at Mercy Hospital, if by "worked" the intent is to convey "was employed by." Many doctors spend time at hospitals without being employed by them. If by "worked" the intent is to convey that while not necessarily employed there she practiced her medical art there, we don't know that either. Maybe she was just visiting someone.