The Book of Ruth identifies Naomi as Ruth's mother-in-law. Naomi, her husband Elimelech, and their two sons Mahlon and Chilion left Bethlehem during a famine and settled in the land of Moab. There, the two sons married Moabite women: Ruth and Orpah. After Elimelech and both sons died, Naomi decided to return to Bethlehem.
Naomi urged her daughters-in-law to return to their own families and remarry. Orpah eventually did so, but Ruth famously refused, declaring: "Where you go I will go, and where you stay I will stay. Your people will be my people and your God my God" (Ruth 1:16). Ruth's loyalty to Naomi is one of the most celebrated examples of devotion in the Bible.
The other options are prominent women in the Bible but have no mother-in-law relationship with Ruth. Esther was a Jewish queen in Persia. Deborah was a judge and prophetess of Israel. Leah was one of the wives of the patriarch Jacob.