Personally I think ghosting can be cruel, but it also depends on the person you're dealing with. I just deleted a long-term online friend from my Skype, so I basically just ghosted her. But we had never met in person and she, like your friend, was very unresponsive to me.

What I personally would do is stop initiating any contact with this person, and let it naturally die out and fizzle. When or if she reaches out to you, you can delay your responses for a long time - like a week or more - and be just as unresponsive, and then be very brief. But don't reach out at all to her. It should naturally die out that way, I would think! She'll get the hint eventually.