Malbim: Then she thought that they merely want to accompany her. Now she understood that they want to live in Eretz Yisrael. She told them that my nation will not marry you. If you will say that I will marry [my sons] to you, for you were already my daughters-in-law, do I have more sons in my womb?! She said so rhetorically (they were already married for 10 years). Surely they would not want to wait for Na'ami to remarry, bear sons, and the sons will mature. By then, Rus and Orpah will be old, and improper for youths so much younger than them!