She is first seen when Ratigan is mad at his henchman, Bartholomew, for accidentally calling him a rat so he throws him outside and summons her with a bell. Bartholomew is heavily drunk, so he doesn't notice her walking up behind him, and remains oblivious even as she picks him up by the tail and then swallows him whole. The thugs reactions when Ratigan is about to ring the bell to summon her, as well as Ratigan's comment of "You know what happens to people who upset me," likewise implies that this was not the first time Ratigan executed a thug for upsetting him via Felicia. In addition, Ratigan also made an implied threat to feed the rest of his minions to Felicia if they didn't continue with their praising song of him.
Later, after Fidget tells Ratigan that he had lost the list he gave him while Basil was on the case, which Ratigan correctly reasons that the detective can use to track down his hideout, he sends Felicia after him and she tries to eat him. But amidst his grousing about Basil messing up his plans, he realizes that since he knows Basil is coming, he can set up an ambush. As such, Ratigan tells Felicia to release Fidget, which she does grudgingly.
When the henchmen arrive at the queen's palace, they use her as a vehicle, and Fidget tries to feed the queen to her. While Basil, Dawson, and Flaversham rescue the queen, Basil's dog, Toby, chases Felicia away. She manages to escape from him by scrambling up a brick wall where Toby cannot follow. Thinking she has escaped, Felicia flicks her tail at him as she hops over, only to be mauled by the royal guard dogs on the other side as bits of fur and the bow in her hair fly into the air.
It is unknown whether or not she survived, although some subsequent comic stories show her to be alive still.
The way Ratigan feeds Felicia with those who upsets him is similar to how Jabba the Hutt feeds the Rancor.
Felicia is similar to Lucifer in the sense that both have been cared for like angels by villains ( Lady Tremaine, Ratigan), are almost seen trying to eat a mouse who is on the good side, and are chased away by good dogs.
Felcia bears some great similarities to Scorch from 101 Dalmatians: The Series, such as both being a pet to the main antagonist (Cruella for Scorch & Ratigan for Felicia), both having the same color scheme, both wishing to eat a character (Spot for Scorch), and that both are voiced by Frank Welker.