Can we pinpoint a turning point in Tolstoy's Anna Karenina

Turning points are difficult in a novel as interwoven and complex as Anna Karenina. One could look at the book as a whole and try and identify a peripatetic
moment and this is arugably nigh on impossible. A better way to examine points of no return is to look at individual charachters and their actions. it makes sense to on our title charachter, Anna Karenina. Her death at the end is so shocking in some ways because it seemed so foreign to the beautiful society lady we met at the beginning of the novel. By looking at turning points we can elucidate her complex charachter and how it is formed through her interactions with the other very flawed, human charachters. One fo the most touching moments that could be cited as a watershed moment is her goodbye to her son Seryohza. Though this takes place only in the middle of the book the finality of the moment and the heart wrenching rupture of the mother and child bond  makes this moment stand out. The nature of the goodbye is almost a hint of the trauma to come. It is also the last time she sees Karenin her first husband. This question could be developed into a long extended essay. For brevity's sake I will finish with saying this is a very open ended question that can be dealt with in a multitude ways. Approaching it from a charachter perspective is one possible way, another way to look at it is through themes. Such as the theme of railways and inevitabiliy of Anna's death. In a novel as complex as this there will never be only one turning point but areas of peripeteia can be illuminated.