I think a lot of her music stems from a constant need to do things on her own. She has said that in her past she was a loner, and her teachers would write comments on her report cards about how she did too many things on her own. She probably regrets that, and since RAINBOW (her ultimate past-forgiveness, embracing love song), we have seen a big change in her lyrics; even her happier songs still had a bittersweet tinge to them, but now she has released some downright joyful songs.

So I feel like what she means when she talks about forgiving her past is that she regrets keeping to herself because in essence she was keeping herself unhappy. By forgiving her past and accepting the love she is given, she is able to find peace and happiness.