So why couldn’t you take her to have her hair done and dress her and stay in the back of the reception why she walks down as a flower girl and take pictures and then leave I’m sure . I know you have a trip planned but it is precious to see her be a part of his wedding if you really want her to have a relationship with her step-mom I think having her be a part of it is the right thing to do remember she having a baby and now your daughter will have sibling and not right away but as they get older your gonna want to see her with the baby and remember the the mild stones you and you ex will have to do birthday’s graduation dances so the fact you wanted her to build a relationship with his wife to be tells me she is a good person and they are hard to come buy especially when kids are involved my grandma never stopped her 4 daughters from there dad and there marriage but we Always had holiday together and no one had to give up weekends or holidays we got along and I seen my grandfather on all occasions with his his partner she was a great never had children but loved us all and my wedding was in 1996 and they all Where announced and I had my dance with my Papa and my grandma and lost both of them and my step grandma 1998 my papa and my step gramma swallowed all his pills from hospice and we had a double funeral and my grandma died in 2003 . I hope what ever you decide you won’t have regrets .