How does McKinnon define “allies”? How is gaslighting a form of epistemic injust

How does McKinnon define “allies”?
How is gaslighting a form of epistemic injust

How does McKinnon define “allies”?
How is gaslighting a form of epistemic injustice? (How is it different than a straightforward case of testimonial injustice?)
What is the “epistemic injustice circle (of hell)” that McKinnon mentions? 
How does the term “active bystander” differ from “ally”?