A contracted spirit would be a close partner to a shaman, and for Ainsley, aside from the teacher-student relationship, she could only have a family relationship with her spirit if she wanted to have a great fit for her.
Even if Ainsley might want to take the first ancestor as her teacher or something, the deep meaning behind this decision still puts people in disbelief.
Everyone in the Sloan Family didn't want to owe Ainsley and burden her too much, but Ainsley resolutely devoted herself to the family and even wanted to say that she would always belong to the family, as long as the people in the family accepted her.
Both sides were thinking about each other, and Ainsley also had a little selfish intention to find the first ancestor.
Once the first ancestor became her contracted spirit, she would be a part of the Sloan family in an 'official' way, lessening her guilt and the sense of distance from the family after her identity was exposed.