They are better off keeping Dwan and letting her develop. She is young and this is her first season as a starting player and playing full games. She is young and Tbirds have improved a lot over the season.
Keeping Dwan means the structure can remain familiar. Brining in Cardwell, who is a dominant player, for her first season downunder and expecting her to just slot in is a big risk. Tbirds are not far off being a serious threat.