At the end of "Annie" (1982), Miss Hannigan is seen riding on an elephant at the party but why wasn't she arrested along with Rooster and Lily for being involved with kidnapping Annie?
Miss Hannigan's redemption is an invention of the 1982 movie, and hasn't been explained by its author AFAIK. From Wikipedia:
Miss Hannigan's redemption at the end is also a new development on the part of the movie – in the musical, Miss Hannigan briefly baulks at Rooster's intention to make Annie "disappear" with his switchblade but is soon lured by his promises of a life on Easy Street. In Meehan's 1980 novelisation, Miss Hannigan shows no qualms whatsoever about Annie being killed. In both of these media, Miss Hannigan ends up being duly arrested along with Rooster and Lily at the Warbucks mansion.
Her "villains wikia" entry shows where she redeems herself:
In the 1982 film version, Miss Hannigan goes with her helpers (who are taking Annie away), and suddenly changes when Rooster is about to catch and kill Annie (who has escaped onto the drawn B&O Bridge) because they didn't tell her that they were planning to kill her and is knocked down for trying to stop him. When Rooster slides back down (due to Punjab knocking him after catching Annie), Miss Hannigan scolds him and beats him with her purse calling him a "reprobate." Rooster and Lily are then arrested. Later, she, now a good woman, and is among the guests at a party where FDR and the First Lady are enjoying themselves.