Here is the background:
My fiance has a step-sister. The step-sister is much older than my fiance (37 years old and he is 23). She grew up without her father (also my fiance's dad), because her father and her mother decided not to get married to each other. However they both found the love of their lives and got married years later.
My fiance's father had been supporting his daughter financially throughout her childhood, and they have a good relationship. My fiance's mother also treated her like a daughter, she loves her as a daughter, and loves her kids as her grandchildren.
However, my fiance's step-sister is rude to my fiance's mother. She expect my fiance's parents do whatever she asks. For example, she expected my fiance's parents to drive 5+ hours to her house to pick her kids up, when she wanted to go on vacations with her husband. It seems like the father will do what she asks, because he loves her and he has guilt for not being there for her.
Another instant was when she received her save the date card, she called my fiance's mother and was angry at her for (1) my wedding date was on a weekend, and (2) we did not tell her we were engaged. In our defense, she does not get a say in our wedding planning, and our save the date is our way of announcing the engagement. Our close friends got the same treatment.
Here is the problem, my fiance does not like her, since she was never in my fiance's life, and she is rude to his parents. We (my fiance and I) don't want to treat her like an immediately family by putting her in the wedding procession or at the family table, but if we don't do it, she will be angry with my fiance's mother (yes angry with her not us).
Sorry I am venting, just want some suggestions and advice on what you guys would do in this situation? Our options are:
1. treat her like family to make her and my fiance's parents happy (the parents are not paying for the wedding)
2. make us happy by treating her like an extended family (same treatment like an aunt or grandma)
