She is the only child of Pureblood parents who spent twenty years trying to conceive. Arabella is impatient, a trait that she’s had since birth when she arrived two weeks early. After numerous miscarriages and years of struggle, her parents were so happy to finally have a child that it didn’t matter when they learned she was a Squib.
Unfortunately, the rest of their world could have cared less that she had managed to survive despite her mother’s health issues and focused solely on her magical status. She stills hears the whispers about Squibs, which equates to ‘worthless’ in the eyes of the majority of her world, but she never lets their words bother her. To do so would be to give power to the prejudice and stupidity that leads to saying such things, after all.
Instead, she spends her life fighting the intolerance and proving her worth as a person, which means far more than the ability to do magic in her eyes. The greatest wizard or witch is unworthy of respect and admiration despite their talents, after all, which has been proven many times in her opinion, but a truly great person is deserving, regardless of their bloodline or magical skill.
That isn’t to say that she doesn’t occasionally fall into the trap of wishing things were different or wanting the ability to do something as simple as transfigure a tea cup. It’s a slippery slope, though, that often leads to frustration, anger, and hopelessness, so she avoids getting close to the edge. There are a great many things that she is good at, after all, so she reminds herself of these when she feels the desire for more than what she’s been given in life.
It’s her outlook on life that first brings her to the attention of Albus Dumbledore and leads to her joining the Order of the Phoenix during the first Voldemort war. She is trustworthy, loyal, and tenacious, which are all traits he admires. It’s easy to listen and pass along information. Squibs are so often ignored that she can easily blend into her surroundings and observe with a keen eye that rarely misses anything. It’s an almost constant fight for respect and to prove that she’s not defined by conventional expectations, or lack thereof, yet she never tires or considers accepting bias as truth, whether it’s about Squibs, Muggles, or Muggleborns.
After the war ends, she accepts her new assignment with pride and can’t help being somewhat smug, even if it is a bad quality to possess. The knowledge that a Squib has been given such responsibility makes her hold her head just a little higher and makes it easier to ignore the slurs at her lack of magical ability. She might not be able to perform a silencing charm or transfigure a tea cup, but that doesn’t mean she’s useless. So she happily moves into a little house on Wisteria Walk, buys a couple of cats, and watches as the savior of the wizarding world grows up two streets away, ready to fight if she’s ever needed.