Siteine has been the assistant coach to Ross Cronshaw since pre-season but taken over head coach duties following Cronshaw's unexpected resignation last week.
McIlroy, development officer for the Suns, said Cronshaw had resigned due to family commitments and he was relocating to Whanganui.
"However, the team are stoked Tania has taken over as head coach. We know her, know how she operates and she doesn't beat around the bush. The team have a healthy respect for her and she gives the team the lift and confidence we need," McIlroy said.
He added Siteine was well-known within the Whangarei basketball community and has been involved in women's, club and national age group teams.
After the disruption of Cronshaw's resignation, the team are firmly fixed on their round-three game against Counties Basketball this Saturday at Breakers Stadium in Auckland.
Counties are a tough team, infused with National Basketball League players such as Dwayne Bailey, Poutu Edwards and Zac Makatologia.
But McIlroy said he feels they are beatable - if the Suns are on their game, which he is expecting them to be. Tip-off is at 2.45pm.