The ending means Anna wins by turning the spirit's own origin against her, though the final shot suggests that the water is not entirely finished with the family. Anna drives La Llorona off for good with a cross made from wood taken from the tree by the river where the boys died, so the weapon is tied to the exact place where the curse began. In my opinion, that is the neatest rule in the film: the ghost is defeated by the landscape of her own crime rather than by a speech or a ritual.
Why does the necklace matter so much? When Anna pulls it off La Llorona during the pool attack, she takes something the spirit treasures. Later Chris holds it up, and La Llorona briefly becomes human and embraces him, believing he is her child. The spell only breaks when Sam uncovers a mirror. It is the best idea in the film, because for a moment the monster is sympathetic, and her grief is the very rule that makes her dangerous. Compare that with Annabelle (2014), where the doll is a vessel for cultists and the threat stays cold and external. Here the villain wants a child, and that makes the scene with Chris more uncomfortable than any jump scare.
Patricia's arc closes on a quieter note. She arrives with a gun, meaning to hand Anna's children over in place of her own sons, since she admitted she prayed for exactly that. Then she changes her mind and lets Anna go. It could be argued that this is the film's only real act of mercy, and it also keeps the story from collapsing into a simple fight between a mother and a ghost.
There is a useful comparison with the main saga. In The Conjuring (2013), Carolyn Perron leans on Ed and Lorraine Warren, and in The Conjuring 2 Peggy Hodgson calls them across from America to Enfield. Anna has no Warrens. Father Perez points her to Rafael Olvera, a former priest who now works as a folk healer, and Rafael is the one who explains the spirit and builds the protections around the house. That swap, a practical outsider in place of the famous investigators, is the clearest sign of how this film differs from the Warren cases, and it fits Michael Chaves's own statement that the film is set in the Conjuring universe but is not an official entry.
Chaves would go on to direct The Nun II, The Conjuring: The Devil Made Me Do It and The Conjuring: Last Rites, all with larger budgets. La Llorona cost $9 million and grossed $123 million worldwide, according to Box Office Mojo. Perhaps the modest scale explains why the finale is a single house, a pool and a cross rather than a full exorcism set piece.
The final shot shows Anna looking into a puddle by the roadside, which hints that the water spirit's influence may linger. The film also links back to the Annabelle story through Father Perez. Perhaps the puddle is the filmmakers leaving a door open, though that is only my reading of the shot, and no sequel has been announced.
