Not much is known about Nana’s relationship with the other administrators but she got called a bastard for trusting a human. Nana told them that there's nothing to worry about and she will make sure that the human will not interfere with their plans. In Chapter 86, Juugo and Roku were sent to destroy her. Meaning the rest of the administrators doesn't trust Nana anymore.
Nana first met Sarina in the hospital and offered her to be a Magical Girl and be the new "Magical Hunter". Then Nana and Sarina meet again in a park where Sarina said that she got the sticks, but Sarina questioned the contradiction about escaping the Tempest which Nana replied that she knows too much and shoots her to death with her invisible bullets.
Nana made Rina Shioi the "Magical Hunter" as she reasoned that Rina has been using her stick long enough. She even trusted her enough to show her information about the tempest. She was disappointed about her being in the hospital with the overuse of sticks and decides to find a new "Magical Hunter".
Not much is known about their relationship but Nana trusts Kichiro enough and made a pact with him a year ago.