- "Gabriella was always an enigma to me. I had never found a human to take so much compassion in her heart that she could dissuade the fact that her family were vampires."
- —Carlisle on Gabriella's compassion
As a human, Gabriella was described as being compassionate, kind, caring, empathetic, friendly, and easy to get along with - the complete opposite of her ancestors Anastasia and Vivienne Blackwell. She is said to be extremely loyal and protective of her friends and family. It has been suggested that she inherited her compassion (a trait she most likely picked up over the years of growing up) from Carlisle. She fights for those she loves, and for what she believes is right. She was also quite athletic, as Gabriella's favorite hobby was dancing, and mentioned on several occasions that she wanted to be a professional dancer. After the rape, Gabriella's personality dulled a bit, and she suffered from post traumatic stress, however with the help and support of her family, Gabriella was able to overcome her traumatic experience and move on with her life. Her bright personality continues to return with time.As a vampire, Gabriella's emotions are amplified, including her compassion towards human life. This helped her to focus solely on the animal blood, as she feared that she would accidentally "slip" and harm an innocent. However, when Gabriella first hunted after completing her transformation into a vampire, she was unable to keep down the animal blood for long and coughed it back up moments after feeding. Because of this, Gabriella was forced to drink human blood out of blood bags that Carlisle took home from the local hospital.
It is later revealed that her inability to consume other sources of blood was unintentionally due to her doppelganger link to both Anastasia and Vivienne Blackwell, as well as the fact that the spell created by the Adriani Line to exterminate the vampire race required Gabriella to be human, which was why her body was rejecting the animal blood.
Gabriella is a very beautiful and attractive young woman with an oval face, almond-shaped brown eyes and long, smooth dark brown hair. She is tall, standing at about 5'6, and has slim figure. She has been noted to wear a special necklace given to her by Edward that once belonged to his mother, Elizabeth Masen. When Gabriella becomes a vampire, she becomes extremely beautiful with pale skin, straight waist length brown hair, and crimson eyes that eventually turn gold after months of feeding on the animal diet. Her appearance changes if she goes long without feeding; her eyes darken, becoming onyx black, and purple brusie-like shadows appear beneath her eyes.
Gabriella has an uncanny physical resemblance to her ancestor and doppelganger, Vivienne Blackwell, who often poses as Gabriella in order to play mind games and trick people. She also shares an uncanny resemblance to Vivienne's twin (Gabriella's ancestor and doppelganger), Anastasia Blackwell, however the two are easily told apart by Gabriella's olive warm skin and chocolate brown eyes, and Anastasia's pale ice skin and crimson eyes. Although Vivienne, Anastasia and Gabriella are exactly the same in terms of physical appearance, there are some slight differences between the three girls in terms of fashion and style, and especially personality.
In terms of fashion sense, while Gabriella was human, she was much more casual, sporty and "girl next door" and didn't like wearing a lot of make up. However, her sister Alice, who thinks that Gabriella should do everything a normal teenager would do (i.e. love to shop, party whenever possible, etc.) doesn't seem to care what Gabriella thinks and continues to buy her designer clothes brought at expensive malls, all the while persuading her to dress up and look glamorous. On special occasions, Gabriella can be seen wearing fashionable dresses with her make up done up by either Rosalie or Alice.
As a vampire, Gabriella's wardrobe changes from a "girl next door" look to a slightly more hip, sophisticated look, trading her usual jeans-and-T-shirt for more dresses, and boots and heals. Since becoming a vampire, Gabriella's physical appearance is said to have a more mature look, giving her a more sexy and womanly appearance. Her hair also goes through some changes, and it changes from straight waist length brown hair to having some red streaks and stylish new waves.
- Gabriella: "How do you differentiate? Wait...do you hear these voices all the time?"
- Edward: "Pretty much. (they hear knocking)"
- Gabriella: "Knocking, okay. I'm hearing knocking sounds."
- Alice: "Yeah, honey, we all are."
- — Gabriella, Edward and Alice on Gabriella's telepathy powers.
Some vampires gain a special ability when they get turned into a vampire. As a result from being raped while she was human, her will to never be helpless again was so strong that in return, when she became a vampire, she gained the ability to mentally control any function of the brain, a power more commonly known as Advanced Telepathy.
At first, Gabriella's ability originally manifested as mind-reading, as she continuously started answering questions out loud that people were just thinking, but she subsequently discovered that she could also send her own thoughts to other people as a form of communication. Gabriella can actively focus on the thoughts of a particular person, but she still sometimes picks up thoughts of random people from within her vicinity, and she can have difficultly "blocking" the thoughts of agitated individuals or crowds. If a person is thinking in a language other than english, Gabriella can still hear them, but she does not automatically understand the thoughts. Because their abilities were so similar, Edward helped Gabriella through controlling her ability. Her control over her telepathy continues to improve with time and practice.
Over time, Gabriella learnt that while she could send her own thoughts into the minds of others as a form of communication, she could also cast telepathic illusions to mislead individuals. These illusions can deceive a target's sense of sight, hearing and touch. She can also erase memories, and lock someone within their own mind, though to a human it can result with them going into a coma. While it is not clear how far Gabriella's telepathy allows her to expand, she is able to locate others by homing in on their thoughts.
Aro originally wanted Edward to join his guard because of his mind reading ability, however after discovering Gabriella and her much more advanced telepathy, his desire for Edward to join the Volturi was replaced with Gabriella. Edward states that the reason behind this is because Aro doesn't surround himself with second best.