Hello, I'd like to help you with your question.
It can be very difficult when someone shuts you out of their life and you don't know why. Not communicating with you is making is harder for you to know why your daughter is upset and how you can address it.
The only thing that is clear is that your daughter feels hurt about something. Whether it is something real or a misunderstanding is unclear. But if you do have that one piece of information, you can build on it to try to communicate with your daughter.
If you have not already, try writing her through email, text or letter and let her know that you love her, care about her and that you are sorry for whatever she is upset about. Let her know that you are not aware of what it is that is hurting her, but you would like a chance to find out so you can fix it.
Another way to communicate with your daughter is through your youngest daughter. If you are close to her and your oldest daughter gets along with her as well, you can ask your youngest to talk to your oldest daughter to see if she can find out more about why your oldest is upset. You can also see if your youngest is willing to act as a go between to see if she can set up some kind of communication between you both.
Also, you can offer to meet in therapy with your daughter. If there is someone neutral there who can help, your daughter might be willing to talk to you. Tell her that you can continue to see the therapist together so you can work this out. Or you will see the therapist alone so you can work on whatever the issue is your daughter is upset about. If she sees you are willing to take her feelings seriously, she might be willing to talk.
If all else fails or you have tried these things before and they did
not work, the only thing you can do is to keep trying. Write her, send cards and photos and encourage your youngest daughter to keep trying as well. Eventually, she should work through this and get back in touch with you.
I hope this has helped you,