Ella j, no advice here sorry, but hugs.
I also have a sensitive 4yo daughter and have just ordered the book pp mentioned.
My dd doesn't interact with other kids much at all. She finds them rough and will often not play at playgrounds if other kids are around. she also gets upset over tiny things, she is very different to her younger brother.
I get quite frustrated with her when she gets upset over the tiniest thing her brother does. I worry that when she starts kindy she will get picked on or won't have friends. It is difficult to see them struggle with these emotions when they are so little.