Matthew Lightwood was an established mountaineer, who climbed mountains by trade and had conquered Everest by the age of 24. One day, when Matthew was about 28, he was staying on a reserve in Africa, preparing to climb Mount Kilimanjaro. Whilst taking a walk around the perimeter of the reserve, he saw a young woman strolling through the lion enclosure casually. He ran outside and climbed into the pen in order to try and rescue her from being eaten. Unbeknownst to Matthew though, this woman was actually Cybele in human guise. When she saw Matthew coming towards her, she quickly commanded the lions to leave them both in peace. Matthew tried to ask her what she was doing, but she was evasive. The conversation quickly shifted focus onto Matthew and he told Cybele of his many exploits, which impressed her greatly. Matthew, smitten with this enigmatic woman, took her back to his room so that they could talk more. They were both attracted to each other in equal measure and it wasn't long before they kissed and in even less time they were having sex. After the event and much to Matthew's dismay, Cybele quickly made her exit and left the room, before vanishing completely. Matthew thought much about that encounter and more questions were raised when Anna appeared on his doorstep six months later.
She was found wrapped in a blanket on his doorstep, with a letter written on gold-embroidered paper. In this letter, Cybele told Matthew exactly who she was, what Anna would grow up to become, and the dangers that she would face as she grew older. She also mentioned, almost as an afternote, the existence and location of Camp Half-Blood, just in case monster attacks became too much. Matthew, who was almost 30 by this point, had wanted a child and eagerly accepted Anna into his life. He still continued his mountaineering career, but had made enough money through publicity and sponsorship to hire a nanny for whenever he needed to leave. As Anna grew up, she went through a cycle of different nannies, each one quitting after finding that Anna was a pain to deal with. Her ADHD meant that she was often climbing the walls, and driving the nanny up them too. She was better behaved at school though, probably because she could use her brain as opposed to staring at the same four walls all day.
The long string of nannies ended when Anna turned thirteen and Matthew deemed her responsible enough to look after herself whenever he was away. He also bought her a pet budgie to keep her company. Due to being a daughter of Cybele, Anna could communicate with the bird, named Eric, perfectly and often had multiple conversations with him, shunning her friends in favour of this interaction. There was a nice status quo for the next two years. Anna was lucky in a sense that she didn't have a monster attack until she turned 13. Matthew was out at a meeting to gain sponsorship, which would last all day. She was sat in her garden, tending to a houseplant, when a scythian draconae smashed through the back gate, entering the garden. It wielded a celestial bronze gladius and advanced towards Anna, slashing furiously. Upon seeing it, Anna screamed for help at the top of her lungs. That cry for help must have been translated into budgie because Eric quickly flew to help her and clawed at the draconae's face. With it thrown off guard, Anna knocked the sword from its hand and used it to stab the monster in the neck, reducing it to dust. The next thing she did was call her dad, to tell him what had just happened. Matthew was in the middle of his meeting but, upon hearing how distressed Anna was, quickly drove home. He kept checking his phone for more information on the journey home, and didn't noticing another car heading in his direction until it was too late.
Anna got a call from the hospital and heard about what had happened. She quickly pocketed her new sword and went to visit her dad in hospital. He was severely injured but put on a brave face and listened to his daughter's story about the fight. He knew that this day would come eventually and was about to reveal all to Anna about her parentage. However, he felt an overwhelming pain and the nurses arrived to treat him. He gave Anna the letter, which he always kept on his person, and was wheeled away. That was the last time Anna saw him. She spent a whole year grieving afterwards, and cut herself off from her friends. She went into foster care, with no other kin. When she was going to a nature reserve with school at the age of 14, she was attacked again, this time by a hellhound. Anna had gone off to be alone, but it had followed her and pounced. Anna was prepared though, and quickly drove her gladius down on its head, reducing it to dust instantly. Then, realising that twice was quite enough, she read the letter like her dad had asked. When Anna read it, it did tell her everything, including the location of Camp Half-Blood.
So Anna used all of the money in her personal bank account to get a flight over to Long Island. She was a day away from turning 16. She was in the forest surrounding camp when a harpy flew at her, claws out. Anna tried to reach out and speak to it, but she got no response. Instead, she ordered an army of squirrels to attack it. Whilst it landed and tried to shake them all off, Anna moved in and cut its head clean off. Then, unwilling to hang around, she ran through the border and entered Camp Half-Blood. She is two days into her time at camp and had turned sixteen. Now, being considered an adult, Anna was allowed to stay there all year round. Now, she had a new family to be a part of and was claimed by Cybele officially on her sixteenth birthday.