Isabel was a young woman with green eyes and shaggy red-brown hair. Her hair consisted of short layers and messy bangs while the rest was kept in two pigtails. She had longer hair and pigtails until one of the pigtails was cut off by others who lived in the Underground City. Prior to joining the Survey Corps, her typical attire consisted of a simple buttoned tunic with a vest and knee-high boots. She also wore a small necklace with a ring tied to it, even when wearing her uniform.
Isabel was shown to be an energetic, outspoken young woman rarely afraid to speak her mind. She was confident in her abilities, and the most cheerful of her companions. She was quite headstrong, shown when she continued to struggle and insult the Survey Corps after she was initially captured. Isabel was also quite prideful, as she once stubbornly refused to tell Levi and Furlan the reasons she came back home beaten with one of her pigtails chopped off.
Isabel apparently did not know how to do math as she stated that it was not as important as feeding yourself in the underground. She valued Levi as a brother figure and became emotional if he berated her. He sometimes calls her an idiot, she takes it personally when he said she was an idiot for not knowing math she nearly cried until he rubbed her hair.
Isabel proved to be a good horseback rider and was able to switch from using her vertical maneuvering equipment to riding a horse with ease. She claimed she was good with animals, and something she had trouble with was humans.
Isabel was born and raised in the underground city. She had lived among garbage in her childhood, which became a norm for her. However, she was then saved by Levi from death at a young age alone, her relatives presumably already dead by the time Levi arrived. She then joined Levi and Furlan's group and obtained vertical maneuvering equipment from them, and became quite skilled with it.
At a later time she, Levi, and Furlan were captured by Erwin Smith of the Survey Corps. When Levi was blackmailed into joining the Survey Corps, Isabel and Furlan chose to follow him. All three resolved to one day claw their way into a better life on the surface.
In a flashback, Levi and Furlan sit in their lodging talking when Isabel stumbles in, bruised and beaten, with one pigtail long and the other side of her hair short. When asked what happened, Isabel claims she fell but Levi questions if she went to see 'low life scum bags' and asks what happened to her hair. She flinches and runs off saying her hair will grow back. Furlan later hears her crying and muttering of killing those who cut her hair off. When Levi walks through the door with a knife covered with a cloth, Furlan asks if he had killed them, and Levi remains silent.
On her first expedition outside the Walls, Isabel assisted Levi in taking down an Abnormal Titan. While displaying an energetic and bold attitude, in truth, she was overcome with fear but felt great courage and morale upon seeing Levi charge into battle.
The next day of the expedition, due to heavy rain, Levi takes the chance to hunt down Erwin, using the rain to his advantage. While his friends want to join him, Levi forcibly demands that Isabel and Furlan leave Erwin to him, stating that Flagon and Sairam's odds are better with them there. After Levi rides off to find Erwin, five Titans, having just devoured another squad, attack the squad Isabel and Furlan are a part of.
Along the way, Levi finds human corpses and analyses them as Titan encounters. He realizes that several Titans' footprints were heading back the way he came. Levi returns to find the Titans attacking the squad with Isabel and Furlan trying to avoid the battle. As they attempt to flee, a Titan jumps out of the fog, causing Furlan's horse to fall back onto his leg, pinning him to the ground. As Isabel tries to assist Furlan in his escape, she deflects the attack of one Titan. She swings around it in an attempt to cut its nape but misses. She gives it a second try, but slips face-first onto the Titan's back, knocking her off balance. Hanging by one wire and barely coming to her senses, she sees a second Titan. She is gripped by fear as it smiles at her and prepares to attack. The Titan launches itself straight at her, killing her on the back of the Titan she was still attached to. Before being crushed between the two Titans, she had been calling out to Levi for help. Her death causes Furlan to turn around and confront the Titans, but he realizes too late that his fall had badly damaged his equipment, and as Levi arrives, Furlan is devoured.
Witnessing the deaths of the first true friends he ever had, Levi goes into a blind rage and slaughters the Titans. Erwin shows up and Levi threatens to kill him, blaming Erwin for the deaths of his friends. When Erwin talks to him, Levi realizes that it was his pride that had blinded him, and leaving his friends behind was the real reason for their deaths.
Isabel, along with Levi and Furlan, stole vertical maneuvering equipment while living in the Underground City. They trained themselves and in time became proficient with it. They were so good that they could evade the Military Police easily, and they looked at it almost like a game.
- Levi - Levi found Isabel among some garbage in the underground prior to the beginning of the story. After that, the two grew so close that Isabel saw Levi as a brother figure, often calling him 'aniki' or 'Levi-aniki,' meaning older brother. Levi was extremely protective toward Isabel, even willing to kill some people who had harmed her and cut her hair. Isabel tended to take any criticism Levi sends to her very seriously, showing how much Levi's opinion mattered to her. When Isabel died, Levi was devastated by the loss of his only friends and blamed himself for their deaths.
- Furlan Church - Having nearly opposite personalities, Isabel and Furlan were often seen at odds with one another. Furlan was calm, level-headed, and knew when things were serious. Isabel, on the other hand, was incredibly hyperactive, persistent, and tended to lose focus easily. Often, Furlan would lecture Isabel or try to be the voice of reason. Despite that, they were close friends with each other and Levi. In their first battle against a Titan, the two were shown to be cooperative and synchronized in their attacks, showing that the bond between them was strong. Isabel died trying to give Furlan time to escape the Titans, and her death made him stop running and face the Titans.
- Hange Zoë - When they first met, Isabel was somewhat uncomfortable with the curious Hange, but quickly developed a better opinion of her when she complimented Levi's skill. Hange got along with Isabel much more easily than with Levi or Furlan, even giving her some sweets as a gift, which Isabel was happy to accept.
- Isabel's name has Hebrew origins, and means "God's Promise." Her surname is a reference to the Magnolia family of flowers.
- Isabel refers to Levi as "nii-chan/san" (aniki in the anime) which means "older/big brother" in English. While they are not related, it is common in Japan to refer to a slightly older male you respect or are close with, as "nii-san."