Liz was first in this scene because she's Ashley's friend and someone for her to interact with. No more, no less. Then I started thinking about what her answer to this question would be and what sort of spells she could get, and things snowballed from there.
That's where a lot of the ideas for the comic in general come from, really. Just considering a bunch of questions based on what's been established and working off what the answers would be. An oddly fitting approach given this storyline and what Pandora's doing.