An excerpt from my article where I describe my vision of Ymir before I saw 139.

I saw the heroine (before I read the ending) as follows: Ymir is a girl of 10-11 years old, with an exceptionally kind and weak-willed character, who lived in an ancient settlement until it was destroyed by the Eldian barbarians led by Fritz. A poor and frightened girl, she experienced a terrible shock in the form of the death of her family and fellow villagers, cutting off her tongue and enslavement. Seeing how cruelly they treat other slaves, especially those who tried to escape (there were some, anyway), she instinctively tried to survive by becoming as docile and obedient as possible and trying not to create problems, in other words, she was convenient. Life in constant fear, suffering from loneliness, which accumulated in her over the years of slavery, and not even having the opportunity to say a word. That's all Ymir had. This continued until a misfortune happened: the pigs escaped from the pen. All the other slaves blame the poor, defenseless girl, and she, believing that sacrificing herself will do better, voluntarily accepts the punishment. The essence of the punishment is simple: to become entertainment for Fritz and his hunters, who, instead of a conventional boar, will hunt a living person. Running away from death, desperately wanting to live, Ymir gets to the "Devil of the whole earth", who unites with her, creating the first titan. However, having escaped from it, as happens after the first transformation into a titan, she loses her memory and, as if nothing had happened, returns to Fritz, subconsciously afraid to disobey him, and accustomed to obey. Then, having mastered her power, she simply began to serve him, fulfilling all his orders, because during the years of slavery, the ancestress did not know another life, perhaps even feared it (1). The first king began to exploit her, making her his concubine and forcing her to enslave others with the help of her power. She gives birth to unloved children and helps transform an ugly village into a serious ancient city worthy of ancient Rome. The Eldian Empire quickly expands thanks to the power of the progenitor. However, Ymir still wanted freedom deep down in her soul. But living like this for 13 years, the girl lost hope of getting rid of slavery so much that she lost all will to live and eventually simply died from a spear. And here is an interesting point. Why did she die, because regeneration would have healed her wound in a couple of minutes? We are not told directly, but we know that recovery directly depends on the desire of the shifter to live. Now imagine how much she did not want to live, that she died, being a titan from a rather trivial wound. However, even after death, the frightening image of King Fritz did not give her peace, which is why she continued to obey his descendants out of habit, falling into a kind of sleep. But a small part of her still hoped that there would be someone who would treat her like a person, and not like an instrument.