Siblings Relationships ?

Thank you all for the input. I am not trying to control my grown daughter by wanting her to come to the graduation. A little back ground story. Their relationship has been more like aunt/nieces than sisters for the most part. But, I have always encouraged all the kids to be active and be involved with each other lives as much as possible. That means the twins have help host wedding, bridal showers for older daughter, have sat through and taken time off work for dgs baptism etc. One of my twin daughters have had a rough few years ( depression, suicide attempts, failing classes) we didn't know if she would even graduate. So this is a big deal to us that she has pulled it together and is graduating.
I have decided not to say anything else to my older daughter about going to the graduation. I have expressed my wish to her that she attends and will leave it at that.
The wedding is on her stepdad's side of the family. Not people any of us hardly ever see or talk with. I was just hurt she would attend something like that and not want to attend the graduation. If she had to work or any excuse then I wouldn't have said a word.
Again than you for the responses.