One of Castle's first meetings was with Cheika, and the new power duo atop the Australian rugby pyramid believe they are not far away from the Wallabies getting back to their best. It will take work.
While a victory over the All Blacks — and a close defeat in Dunedin — showed the side's potential, there were too many lacklustre results in 2017 for the Wallabies.
Twice they lost to Scotland, including a record 53-24 defeat, and also fell to a heavy 30-6 defeat to England on an uninspiring end-of-year tour.
If sub-par results continue, Castle is not afraid to make changes to current plans and to challenge Cheika on the big calls.
"The importance as the chief executive has to be to know what the right questions are to ask. I think my experience in high performance, not just in the last 10 years but certainly over a long period of time is a good thing, because it helps you to be able to ask those right questions."
That experience as CEO — six years with Netball New Zealand and a stint with the Canterbury Bulldogs — makes Castle adamant that her background can provide a neutral, fresh look at the strengths and ailments of Australian rugby.
"I don't have any allegiances — everyone across Rugby Australia feels they'll have the opportunity to build a relationship with me, [it] is really important. I think that was something that the board saw as a real benefit," she told D'Arcy Waldegrave on Radio Sport.
One of her first challenges will be to ensure a brighter season from Australian Super Rugby teams, after a year where Australian teams went winless in 26 games against New Zealand sides. Castle believes that fewer teams will lead to more competition next year.
"I think that's a challenge that Sanzaar recognise, and we all need to be looking at that.
"The depth issue I think will change now with going to four teams — that means we'll have four teams that are more competitive."
Being competitive will not be good enough for the Wallabies however, and Castle remains committed that the future is bright for the Wallabies.
"There were some really good signs — while we didn't win the Bledisloe, that's a real target."
If Castle can contribute to the Wallabies snapping their 15-year Bledisloe Cup drought, she could quickly become persona non grata in New Zealand, but that doesn't worry her.
"I will be wearing my yellow scarf proudly, no doubt about that."