This is an allusion in the Bible to 1st Corinthians, chapter 6, verses 19-20. It reads, "(19) What? know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own? (20) For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's." In these Bible verses, the body is considered a holy, sacred being, just as a temple is a holy place. You are supposed to take care of it and use it to honor God. Some religious people believe this is why people shouldn't get tattoos or body piercings.
When Jazz refers to "decorating her temple," she's referring to how she has decorated her body with her tattoos, piercings, and the clothes she wears, generally how she looks. One message the author is giving us is not to judge others by their appearance. The appearance of the two girls doesn't honestly represent where they come from or what kind of person they are. They both learn, however, that they do have certain things in common, as girls and as human beings.