Advice Please

My Sister in law (husband`s sister) is getting married. I have known her since she was about 9 years old (about 17 years). We have always been very close and I have been there for her through all that girls go through growing up, yet I was not asked to be a bridesmaid. I am a bit older than her and her friends (not sure if that is a reason). One of her bridesmaides is the wife of one of the groomsmen she has only known a couple of years. She has not said anything to me as to why I am not part of her wedding, yet felt the need to explain that the wife of the groomsmen helped pick out her ring, and they have grown closer since!! I am smart enough to know that my feelings being hurt by this is normal, and I am not going to say anything to her about it, because....as I have told her many times already while planning this wedding (she is always asking my advice on things).....it is HER wedding and she has to be the one who is happy on that day, and she doesnt have to make everyone else happy too.
So here is my question.........It now seems that the photographer is asking her to find him an assistant (who knows the family etc) so when it comes time to take the pictures, there is someone who knows who is who, and will be able to round them up so they don`t miss the pictures. She has asked me to be this person. She would also like me to stand by the guest book and make everyone signs it. I feel completely insulted by these requests. Aren`t the bridesmaids there for a reason? Shouldnt they have some responsibilities that day? And what about the groomsmen and ushers? Aren`t they there to help?