Bella didn't have many memories of the time she spent after her brother departed from the world.
She remembered her days in isolation when she was hunting beasts as a source to keep herself engaged. She wanted to not dwell on her loss, or she knew she would lose herself and also the chance of reuniting with him.
The best source of finding a way to meet her brother was to extend her contact with people. She realized that there were unique and different abilities that each individual possessed—as such, she recognized the need to expand her reach and bring more people under her command.
Around that time, she was in Vegas, where she started building her Empire and recruited people who worked for her tirelessly so they could expand her territory. Within a few years, there was no ruler left in Vegas who dared to defy Bella.