Not much about her relationship with her uncle, but they get along very well. Fiona's uncle calls her "Fi" out of affection.
Fiona is one of Robyn's most loyal personal followers, as seen when despite being a top graduate from Atlas Academy and having the chance of obtaining a high paying and high profile job in the Atlas military, Fiona instead chose to follow Robyn in attempting to better Mantle, a cause that Fiona takes immense pride and loyalty in as seen in the victory party in "A Night Off" where Fiona shows clear strong emotions in stating her belief and faith in Robyn's political aspiration to become Mantle's "voice" in the council of their Kingdom and continue helping the city.
Robyn, in turn, reciprocates this loyalty, as seen when she worriedly tried to help Fiona after she was injured by Tyrian Callows during the events of the failed victory party and showed clear anger at the fact she was injured.
Joanna is Fiona's teammate. They are almost inseparable and they are rarely seen apart most of the time.
In "Pomp and Circumstance", they can be seen spying on Atlas military, and later work together with the rest of the Huntresses in "Sparks".
Joanna and Fiona share a friendly relationship as seen in "Refuge", in which Joanna puts the upmost faith in Fiona's ability to coordinate the Huntsmen aiding in their plan to keep the civilians of Mantle safe in its crater. Similarly, Fiona is playful with Joanna, asking why she isn't leading that effort after the taller Huntress took charge of their mission.
May is Fiona's teammate.
In "War", Fiona and May exchange information about their teams' whereabouts.
Fiona is thrilled to see that Ruby's Group safely made it out of Atlas, but seemingly finds it difficult to believe that the now-separated group would be as effective than the entire party. Despite this, the groups work well together, where Fiona helps direct Yang's group with Mantle evacuations.
After an encounter with The Hound, Fiona loses touch with this team.
When Fiona says she hadn't believed that the group is as effective as before, Yang acts offended by the remark. Regardless, the two work very well together, only Yang's Group eventually leaves Fiona's operation without a word as to why, when in truth Oscar Pine had been kidnapped.