Unfortunately, I doubt that is the route it is going to take. The Queen made it clear that she wanted to have "tea" with the Green Witch. Ciel has to deliver Sullivan to the Queen, if she doesn't end up dead at the end of this arc. I don't think she'll be living at the manor as some would like to believe, given that the Queen made herself pretty clear in that letter.
She may be like Soma, who we rarely ever get to see in the manga.
Soma???
Yeah, remember the purpled haired Indian Prince that sees himself as Ciel's friend. Remember this guy: http://static.tumblr.com/55e2c04579193ec2f21638c92792734b/zpdclrc/OUDndnbo7/tumblr_static_eipfu8e9u00g8co400gssc8gg.png
Loll the Indian prince
I really hope that Sullivan and Lizzy get to be friends in the manga. Wouldn't that be cute?!? Seeing those two dorks decorating the manor (Lizzy's all pink and girly while Sullivan's is black and gothic) and tormenting the servants (and Ciel) together!!!!