The similarities between Gretchen and McCluskey's dog are very apparent in the novel, and there is rather apparent symbolism by what happens to both of them by the end of the novel. In the beginning of the book, Gretchen and the dog are both trapped in an abusive and harmful relationship with their "owners"*, and mistreated physically, verbally, emotionally, and psychologically. When Cal offers the dog an escape from McCluskey's yard, he can't comprehend leaving, and enters back into the yard. Gretchen is similar in the way that she can't comprehend telling anyone about her father's abuse, or being free from his mistreatment. Where Gretchen and the dog differ is their ability to "change their fate". The dog needed someone to free him from his yard (like Cal's father, who calls the Humane Society) to escape his abuse. Gretchen had the ability to testify against her father, which eventually helps with the claims against him to prove him guilty, though Cal's intervention made this possible. Gretchen is so strong and brave for enduring what she had to, and like McCluskey's dog, she was able to live in a new, safe environment (foster parents) after she was freed. Both the dog and Gretchen faced mistreatment, neglect, and (most prominently) abuse, which had a great effect on every part of their part of their lives.
*Though it's sick and incredibly sad to view Gretchen's father as her "owner", that is the abusive relationship he forced upon her. He was a dictator of who she saw/talked to, where she went, and every other aspect of her daily life, not to mention how he assaulted, raped, and harmed her physically and emotionally at home. In many ways, Gretchen was not able to have a life of her own, and Otto was thus her captor and a sick, horrible person that owned so much of her childhood.
*Though it's sick and incredibly sad to view Gretchen's father as her "owner", that is the abusive relationship he forced upon her. He was a dictator of who she saw/talked to, where she went, and every other aspect of her daily life, not to mention how he assaulted, raped, and harmed her physically and emotionally at home. In many ways, Gretchen was not able to have a life of her own, and Otto was thus her captor and a sick, horrible person that owned so much of her childhood.