Sudden shift in her behaviour wasn't bcz she was changed or anything suddenly. It was due to fear of losing her son. There was a big communication gap between mother and son and it was also Pobmek's first time when he actually expressed his emotions before he left with Sun. When she heard about her son's accident...at that point she realised her ways can make her lose pobmek . She is very strict for her son bt it's not bcz she hates him bt she thinks what she is doing is the best for her son. She is an example of many typical Asian parents who think that what they are doing is best for their children and want their children to succeed or to be better than others. Bt they don't realise they themselves are making their kid's life miserable by constantly comparing and imposing their own selfish demands and thoughts.