Jacqui
I'm generally not a huge fan of original characters, especially when they form most of the plot. They are necessary, but unless they are the latest rendition of The Big Bad, they tend to be either one-dimensional plot devices, obvious Mary Sues (and the male counterparts) or just not gripping enough for me to care that deeply about them. There are, of course, delightful exceptions to the rule.
Jacqui's characters are beautifully rendered. They have history, stories of their own that we get only glimpses of. You get the feeling that, should she so choose, her characters could leave the Buffyverse altogether and thrive. She has obviously taken the time to get to know them herself, and the effort pays off in diamonds.