Sonia was Todd Alquist's housekeeper. He killed her when she discovered hidden money in his apartment.
Todd brings Jesse to his apartment so he could help him dispose of Sonia's body, whom Todd strangled to death after she discovered his hidden money stash. The two roll her up in a carpet and drive her out into the desert, where Jesse buries her. Afterwards, Todd says a few words as a eulogy to Sonia, describing her as an excellent housekeeper.