I think in these chapters there are several changes.
The first one is that in the beginning of the book, Sara did not care about anything except her appearance. However, when she knew that Charlie was missing, she spent all the effort to find him. And also when she knew that Charlie was near her, though she was totally tired (p.114), she did not give up finding Charlie (p115), as if Charlie was the best ruby of her life. She eventually realized that in her whole life, there was not only herself, so she should pay more attention to the people near her.
Secondly, formerly Sara thought that Charlie was a burden to her, and always complained about him. However, when Charlie was found again, she just comforted him rather than blame him, as she found out that actually Charlie has already been a part of her body, and she cannot abandon him in the rest of her life. (P115)
Thirdly, Sara wanted to be like swam, maybe because she wanted to have beautiful appearance like swam and she wanted be free like swam without caring so much about Charlie. However, when she found Charlie at last, she did not feel in that way any more, since she knew that every thing in her life must be cherished. (p125)
The last one, it is so hard for Sara to admit her fault before, but finally she can explain the real situation to her sister and accept the fault. She realized that everybody make mistake. It is common, but it is also important to accept that. (p126)