Getting married. Need help

Wedding is coming up this summer. My fiancé is the most giving woman I have ever known. She has done more for her family than anybody I know. Whether it's helping when people are sick, Taking grandparents to doctors, helping nieces and nephews with homework, just randomly getting small gifts when she sees something that she knows will make people smile, I could go on and on. There is not a selfish bone in her body. She actually confided in me that she felt selfish for being upset that nobody in her family is being enthusiastic about the wedding. She's got her sister who has her own life problems as we all do and her mother who won't be part of anything unless it's done on her terms. In short we are planning the wedding ourselves, but I feel that there are certain things her family should be helping her with and they are just not stepping up. For example she's got an appointment to try on her dress and has nobody to go with her from her family. I'm sure my mother and sisters will offer, but it's not the same. She really wants her mother and sister to be involved. She does so much for them and it's killing me that they are not being there for her int his one very special time that she needs and wants them. My question is, would I be crossing a line if I called the mother or sister and told them how upset my fiancé is and that it would really mean a lot if they could call her and offer help? I wouldn't be nasty about it, it's just so painful to see her face when she gets off the phone and yet again there was no mention of the wedding or worse yet when she brings it up and they change the topic. I did ask the mother and father for approval to propose to her even though we're in our 30's. They both hugged me and told me they loved me and were so happy and that she finally found me. The mother cried to me that she was so happy. I don't know if they even realize how hurt my fiancé is over the lack of family support.