Just wanted to offer a possible idea regarding her wanting to be alone. I wonder if you could quietly say to her, "I'm going to give you some time alone, but I'm going to be coming back to check on you every few minutes or so because I love you, and when you are ready, I'd like to help you".
You can determine how many minutes based on your knowledge of your daughter and what you can handle. If you wait too long for your own comfort, it will probably raise your anxiety (it would raise mine!) and make it harder to do the next step calmly.
When it's time to check on her, poke your head back in and say as quietly and neutrally as you can, "I'm just checking in to see if you would like some company yet". If she says no, or doesn't respond, then say in the same neutral tone, "ok, I'll check back again in a little while".
By keeping your tone neutral (rather than hurt/upset) you are establishing that there is a calm, caring adult who is ultimately in charge. When I say "being in charge", I'm not talking about establishing power, it's about establishing certainty/safety. As you voiced in one of your posts, you want her to know that she can trust and depend on you. If you are able to be the calm in the center of her storm (not an easy task) then she will know that there is a safety net when she is ready for it.
The hardest part for you if you try this, will probably be walking back out the door each time without reacting. However, if your response becomes predictable and feels non-judgemental and caring to her, she may be able to start letting you help her sooner in the process.
Another thought is, if this seems like an approach that works well for both of you, you could talk about a mid-way signal. Maybe she could hang a sock on her doorknob, or set a teddy bear in a particular place if she wants to let you know that she is ready for you to be in the room but not yet ready for you to come too close or to interact with her. The agreed upon signal could mean that when you check on her you go and sit somewhere in her room where you are nearby. When I use this approach I bring a book or something else to do so that I'm "there" without being obtrusive or invasive.
I really feel for you--it's emotionally exhausting to support someone who is really upset, and doubly so when they make it difficult to help. I hope you know that your daughter is lucky to have you. It's easy to see from your posts that you are a loving parent who is willing to go the extra mile to help your daughter. Sometimes it's easy to lose sight of what we are doing well when we are frustrated or not immediately effective with what we try. Really though, it's the loving and the continually trying that makes the difference in our childrens' lives.
