I don't know if she coined the terms, but Doreen Virtue would be the best place to start. She has at least two books out on the subject, an FB page, and other related material.
Now, I've tried contacting her as well to see if she might accept the idea that Earth Angels could also be like something else called "Otherkin" but wasn't able to get my message through (that I know.) There's overlap between the two, though you'd have to know both concepts well to notice that much
Hope that helps!