Ways to include future husband's step-sister in the wedding

My fiancé has a step-sister who has been in his life for a very long time. He was 4 and she was 9 when his father and her mother married. The step-sister's father died when she was 5, so my future father in law has been pretty much been the only father figure she's had throughout most of her life. My FH has two older brothers. My future husband is close with her, but is having trouble trying to figure out ways to include her. He's someone who is still stuck on the idea of just having guys on his side of the wedding party so he didn't include her as a groomswoman. Both of FH's brothers didn't include her when they got married and my future father in law told my FH several years ago that he was hurt about the other brothers leaving her out because he does view the stepsister as his daughter. FIL said that the did want to adopt the step-sister after he married his second wife, but he didn't out of respect for the step-sister's paternal grandparents who had regular visits and she also spent part of the summers with them. FH and I are considering having her as a reader or something else in the ceremony. We are trying to make it not seem like consolation prize for her.