Who is Uhmma from A Step from Heaven and what is their importance?

Uhmma grew up in a wealthy family in Korea. When she married Apa, she gives up her life to join his. He owns a fishing boat and works as a fisherman. The couple lives with Apa's mother in a hut in a poor village. Uhmma is a dreamer. She longs for something better. She convinces Apa to ask his sister to help them immigrate to America. Apa finally relents and writes to his sister Gomo. Gomo is able to help them come to America, and the family lives with her for a while.