In my opinion, what you have encountered is not unusual. Many Korean's carry a lot of baggage and often they wish it to stay unknown. It may be from actual fear, or wariness regarding reprisals or shame and embarrassment. From a western perspective, the reasons for their silence frequently seem illogical. That is due to the very real difference in values and the priority of the various values in their lives.
My wife is a Korean born during the Japanese occupation. Her family was far flung and close relatives lived in what today is North Korea. The family was affluent and we suspect her mother was Japanese. Some members of her family were involved in one or the other resistances/independence movements following the Japanese departure. Her mother died from unknown causes and her father subsequently and suddenly died or was assassinated. She was orphaned a total of 2 times, abused, mistreated and stripped of her inheritance before her teens. What she did to survive she has never told me entirely.
From this brief summary there are several reasons she might not want to talk about her past in addition to it just being painful. In the least it appears that her family were collaborators during the Japanese occupation which is still a very sensitive subject in Korea. She would not want to discuss relatives in North Korea due to possible repirasals against them by the government or possibility of the leveraging the North Korean realtives against the South Korean portion of the family. Also what she might have had to do to survive might cast her in a dishonorable light no matter how justified her actions.
It has taken me over 40 years to piece together most of my wife's story. In your case I suggest you continue to be patient . You will not get the whole story at one time, You will get it in bits and pieces like assembling a puzzle. From time to time you might check if the pieces are assembled correctly or if your conculsions are correct. Again take your time, You may be rebuffed in these enquires. If so revist on another day and time. Eventually you will get the entire story or at least the story she is comfortable with you knowing.