I hav a 16 year old a 12 and 11 year old I wouldn't allow them to travel 3000 miles alone.

However I might have considered accompanying them myself.
Funny things get said about people when they up sti cks and move. It's very common for all sorts of stories to go around about why they left. Sounds like it's possible this happened when you left.

On a different note, believe me I know how hard it is to watch your kid feel alone.
I have four kids who all have friendly acquaintances at school they have never had close friends until they reached the middle of high school.
Playground politics are brutal, especially amongst pre teen girls. They can drop friends for seemingly no reason and it's as though everyone else smells the blood in the water and know not to go near.
My eldest daughter suffered terribly in primary school from around 7-11. And it was heartbreaking the first year in high school wasn't much better.
I had to encourage her to just focus on her work, And tell her that when she found something that really interested her she would find her true friends there.

It was true enough, she had a passion for Asian culture and that's where she made her closest friends.

But it is hard, maybe you could ask her how things are different where you are now to where you came from.
Her perspective might give you insight into what's going wrong for her.
All the best. Take care.