3. Take responsibility for your past words, actions, and promises
Maybe you're not absorbed in a demanding job, you didn't get back together with an ex, and there's no concrete, legitimate explanation for why you don't want to see this person again. One of the reasons that ghosting is so confusing and painful for the ghostee is that it often comes out of nowhere and is a dramatic shift from where things seemed to be heading. One day a guy is snuggling on the couch with you watching a Girls marathon and making plans for the future, and the next he disappears into the texting ether, making you feel like he never existed at all.
Listen, we all have our issues! But if you've misled someone to believe you were interested in more and then all of the sudden never want to see her again, you need to own up to it -- even if you can't totally articulate why. Saying things like, "I know I promised to [insert past promise], or when I said [thing that sounded like we had a future together] it made you think that I wanted to be in a relationship, but I tend to do that and then freak out when things get serious or more intense. It's an issue that I have and I apologize if it caused you any pain." By doing this you'll be validating the confusion and hurt she's feeling and taking responsibility for your part, so she doesn't go on blaming herself for your sketchy behavior.