In Southern California, shortly after the Mexican-American War, a Scots-Native American orphan girl, Ramona, is raised by Señora Gonzaga Moreno, the sister of Ramona's deceased foster mother. Ramona is referred to as illegitimate in some summaries of the novel, but chapter 3 of the novel says that Ramona's parents were married by a priest in the San Gabriel Mission. Señora Moreno has raised Ramona as part of the family, giving her every luxury, but only because Ramona's foster mother had requested it as her dying wish. Because of Ramona's mixed Native American heritage, Moreno does not love her. That love is reserved for her only child, Felipe Moreno, whom she adores. Señora Moreno considers herself a Mexican, although California has recently been taken over by the United States. She hates the Americans, who have cut up her huge rancho after disputing her claim to it.
Señora Moreno delays the sheep shearing, a major event on the rancho, awaiting the arrival of a group of Native Americans from Temecula whom she always hires for that work. She is also awaiting a priest, Father Salvierderra, from Santa Barbara. She arranges for the priest so that the Native American workers can worship and make confession in her chapel, rather than leaving the rancho. Ramona falls in love with Alessandro, a young Native American sheepherder and the son of Pablo Assis, the chief of the tribe. Señora Moreno is outraged, because although Ramona is half-Native American, the Señora does not want her to marry a Native American. Ramona realizes that Señora Moreno has never loved her and she and Alessandro elope.
Alessandro and Ramona have a daughter, and travel around Southern California trying to find a place to settle. In the aftermath of the war, Alessandro's tribe was driven off their land, marking the beginning of European-American settlement in California. They endure misery and hardship, for the Americans who buy their land also demand their houses and their farm tools. Greedy Americans drive them off from several homesteads, and they cannot find a permanent community that is not threatened by encroachment of United States settlers. They finally move up into the San Bernardino Mountains. Alessandro slowly loses his mind, due to the constant humiliation. He loves Ramona fiercely, and regrets having taken her away from relative comfort in return for "bootless" wandering. Their daughter "Eyes of the Sky" dies because a white doctor would not go to their homestead to treat her. They have another daughter, named Ramona, but Alessandro still suffers. One day he rides off with the horse of an American, who follows him and shoots him, although he knew that Alessandro was mentally unbalanced.
Ramona was missing from the rancho for two years. Felipe Moreno finds the widowed Ramona and they go back to Señora Moreno's estate with Ramona's child. Felipe has always loved her and finds her more beautiful than ever. Although Ramona still loves Alessandro, she marries Felipe and they have several more children together, although Ramona and Alessandro's daughter always remains their favorite.

Question: Why does Senora Moreno hate Americans?
Answer: They cut up her rancho after disputing her claim to it.
Alternative answer: Took over her Ranch