This is a personal response question. It is up to you how you would like to go about writing five poems that deal with the book Chains. Personally, I would start out by figuring out which type of poem you would like to write. You can pick anything, but I recommend the poetry style somehow fit with Isabel and her situation. I would choose haiku.
A haiku is three lines long. The first and third lines have five syllables. The second line has seven syllables. It doesn't even have to rhyme. Traditionally, a haiku emphasizes "simplicity, intensity, and directness of expression." That would work well for Chains, because Isabel's situation is intense. Madam Lockton is a horrible slave owner, and Isabel suffers greatly because of it. Madam Lockton has Isabel branded on the face at one point. Madam Lockton also has a nasty habit of making sure that Ruth and Isabel say as little as possible. A haiku works for Isabel's situation because it forces you to say a lot of emotion in very few words.
I also think haiku is a good choice, because poetry is mentioned several times in the book. Specifically, Isabel mentions that she has never read a poem before. That's partly because she is intimidated by the concept. She worries that she isn't smart enough to understand the words on the page. A haiku can carry complex emtions, but it is visually accessible, because it is so short. I believe that a haiku is an appropriate poetry format for Isabel.
For poem topics. I would focus each poem on Isabel and her emotions. Pick five events in the book that Isabel feels strongly about. At the start of the book, Isabel thinks that she is now free. That has great poem potential. Write another poem about how she feels about being sold to the Locktons. A third could be about Ruth's sale. A fourth could be about the conditions in the prison. The fifth could focus on how the war makes her feel. A sixth could be about the branding incident.