Dunedin-based Southby co-coached the team with Natalie Avellino this year, but the franchise decided to revert to a traditional structure for 2013.
Southby will be the boss and Avellino will be her assistant.
Southby is excited about the opportunity the Steel role presents.
"Obviously, the focus is now on contracting players to enable us to keep building on the platform we established this season," she said.
"I know from a results perspective we didn't achieve as well as we would have liked this year but there was a lot of growth and development in the players - often in ways the public don't get to see.
"The learning which occurred this year will be very beneficial to the Steel so it's paramount we retain our nucleus of players as well as adding strength where needed to continue moving forward towards our ultimate goal of winning the ANZ Championship."
