One of Felicity's defining characteristics is her strength, both physical and emotional. However, any reminder of "weakness" she has shown in the past (for example, her father's sexual abuse of her as a child) causes her to become enraged or depressed, or both. She is constantly trying to strengthen herself, and gives her greatest desire as "to be too powerful to ignore. As such, she is the most popular girl at Spence Academy, and in A Great and Terrible Beauty often hazes Gemma and Ann as a senior would do to those younger than her.
Felicity's father is Admiral Worthington, who is famous for his good looks and heroic deeds in the navy. He is also a pedophile. Felicity's mother is Lady Worthington, who left their family for a French artist in Paris. Felicity also has a younger cousin named Polly, who Admiral Worthington took in at the age of six. He also chronically abuses her. When, in The Sweet Far Thing, Felicity and Gemma encounter her, she is severely depressed and seems to be confused about the difference between her and her doll, who Admiral Worthington tells her is a wicked reflection of herself.
Felicity also suffers from feelings of guilt and self-loathing because of her romantical feelings for other girls. In the strict Victorian society, she has been told that homosexuality (being lesbian) is wicked, and that she is "degenerate." She also feels guilt because of her father's sexual abuse of her, as a small child-- he told her that she "[brought] it out in him," and so Felicity grew up blaming herself and trying to believe that her father really did care about her as his child, and not just as something to abuse.
One of Felicity's most prominent characteristics is her bold sexual manner, which is mostly displayed in A Great and Terrible Beauty., brags to her friends about how many men she plans to have, and regularly meets Ithal, a gypsy boy, in the woods. Although not proven, this can almost certainly be traced back to her abusive childhood, when after she grew to be 'too old,' her father completely ignored her.
Felicity's personality bears a strong resemblance to Gemma's mother's friend Sarah. Unfortunately, Sarah went mad when she felt that she was losing the power of the realms and became Circe. Sarah showed signs of paranoia and jealousy of Gemma's mother Mary, both of which Felicity has occasionally shown of Gemma, though she was quick to hide it (Gemma can enter the Realms on her own, but Felicity can only go if Gemma takes her, a fact she resents as she hates being dependent on anyone). Finally, Felicty's act of ruthlessly hunting and sacrificing a deer to gain access to the realms parallels Sarah's sacrifice of a Gypsy child; the parallel is heightened by the respective narrators' (Gemma and Mary) feelings of anxiety and foreboding.
Unlike Sarah, however, Felicity does not betray Gemma. Felicity has a strong sense of loyalty; when forced to permanently choose sides in The Sweet Far Thing, Felicity stays with Gemma and Ann-- though Pippa, with whom she is in love, is on the opposing side. Felicity's loyalty comes out in many other ways-- she is always quick to defend her friends, both verbally and physically, when they are threatened in the Realms but can be hypocritical.