This name has its roots in ancient Egypt. Goddess ISIS, mother of Horus who was the only one to know the actual name of Ra. The ancient Greeks added the "dora" part of the name which in Greek means "the gift" so the meaning of the name is The Gift of Isis, much like Theodora means God's Gift. The second meaning is again derived from Greek word for IRON which is SIDERO, so the meaning could be The Iron Lady.
The second meaning is again derived from Greek word for IRON which is SIDERO, so the meaning could be The Iron Lady.