Your d is doing so well!
Look at these positives:"She is no longer the scared, bewildered, skinny, scrawny LITTLE girl that she has been her entire high school career, but instead a beautiful, vibrant young woman. " WOW So amazing!! And well you should be so proud and YOU did this kkhrd!!
I find the adolescence really can bring out the mean/competitive side of many of us. Who can really say why these girls do that, but I alway wonder if they themselves are so insecure, they act that way to feel powerful. It is not power it is cowardice, imo. I sometimes feel badly for them. It makes me wonder what that other girl is going through that she needs to do mean things. If it is really bad, is there where a discussion with the school or her parents may be required. I had to do that with my ED d age 12 in grade 7 here 6 months into ED! This girl and her brother were screaming racial insults at her... well that is another story!
Is there another group of girls your d can hang out with? what about other girls that belong to the same clubs she belongs to? Maybe inviting one of those girls over may help.
The thing about cheer, would it be something to discuss with the coach? I know girls want to keep it private, but just making sure it is not something that she needs to tell the coach. Are there other girls on cheer that she gravitates to?
Your d is a leader. She is full of light and love! I see that in this:"She does do so much volunteer work, but mainly through her school in clubs for Habitat for Humanity, Operation Smile, and community garden. She's also edits the school paper and a literary magazine. She is a eucharistic minister and an angel ambassador"
I know it is awful, she has just been through H3!! and so have you. I have PTSD from my own high school years, and worried/worry so much about my kids going through the same. And as YOU know what is right and wrong behaviour toward others, she knows too. That is golden and she will internalize your nurturing to give her support in those stressful times- you may not see it yet but it will come. I have told my daughters when something like this has happened (yes a few times here with both Non ED and ED d) that we can see how they are suffering so that is why they lash out.My oldest d non ED was bullied/abused in her final year of high school, so I do understand how horrific it is to see them in emotional pain. It helped both my d's gain some perspective, empathy and forgiveness and it helped to lighten their angst to see those people as suffering within themselves. I have used the knowledge that some friends we need let go in love and kindness and others will come to us with love and kindness. It helped my kids feel less upset. It helps me to remember that too! To know that we have different friends at different times for different reasons is normal. I know it is so hard right now. It really does suck!
I am not sure if anything here helps you. But this too shall pass and it may be a time for your d to move forward with other people that are more supportive. She may just have to ask another girl that she never thought would be a friend "around the corner", to hang out, go shopping, etc..
That other friend is there, I am sure!
Our hearts really do break when they are in pain. And with ED the pain is more poignant, I think. They have been through enough physically and emotionally and we just want it all to be fine. I am sorry this is happening.
(PS I still cannot watch any Mean Girls movies- too painful for me personally! 😔)