How the fuck she convinced herself tht she did wrong? All this years he ignored her, took he for granted, expected her to cook and clean while both worked, made her explain to HIS mother why she wasn't getting grandchildren and all sorta of bs... and in the end he slept with someone else. Her only mistake was not divorce properly before investing in her relationship with Niina.
If she ends up alone and bitter, THAT'S will be all her own fault.