She was voiced by Lianne Marie Dobbs.
Marilyn appeared pursuing Diancie as it searched for Xerneas. During Yveltal's rampage in the Alearth Woods, her Delphox and Yanmega were turned to stone by Oblivion Wing. Despondent over the loss of her Pokémon, Marilyn was comforted by Riot, whose Greninja and Ninjask had also been affected. Just as she accepted Riot's affection, Yveltal aimed Oblivion Wing at them, and they embraced shortly before being killed. Xerneas later brought them back to life using its Fairy Aura.
In the credits of the film, Marilyn gives up the life of a jewel thief for honest work at a clothing shop. Riot visits her at the shop and proposes marriage, which she most likely accepts.