One of the three Chasers on the Gryffindor team during most of Harry's years at Hogwarts. Oliver Wood considered her to be a superb Chaser (PA8), along with Angelina Johnson and Alicia Spinnet, who are a year older than Katie (OP26). As a member of the team, Katie has taken her share of rough play, including a time when Montague of Slytherin intentionally grabbed her head instead of the Quaffle, nearly unseating her (PA15). Katie, along with Alicia and Angelina, joined the DA (OP17).
During his first practice as Gryffindor Keeper, a nervous Ron passed her the Quaffle so hard that she missed the catch and was hit in the face, causing a nosebleed. Fred then accidentally gave her what seems to have been the wrong end of a Nosebleed Nougat -- the one that causes nosebleeds rather than arresting them -- so that eventually practice had to be called off when Katie didn't stop losing blood (OP14).
Katie had more bad luck in the fall of 1996 when she was placed under the Imperius Curse by Madam Rosmerta to carry a cursed opal necklace to someone at Hogwarts. The parcel broke open as she argued with her friend Leanne. When Katie touched the necklace her body levitated as she writhed in pain, and then collapsed (HBP12); she had to be evacuated to St. Mungo's (HBP13).
In May of 1998, Katie returned to the school to fight in the Battle of Hogwarts (DH30).
Lexicon reader Andrew Wells wrote us to point out that Katie -- like Harry -- must have played on the Gryffindor Quidditch team in her first year. This contradicts Ron when he says first years "never" make the house teams (PS9). But this is a common mistake fans make, confusing Alicia Spinnet with Katie. Alicia was a reserve player the year before, in her second year. Katie played her first ever game alongside Harry. See Steve's explanation here.
In the movie of Harry Potter and the Half-Blood Prince, the role of Katie Bell was played by Georgina Leonidas.