Upper mid-level, yeah. Still a big threat though, or at least enough of one to be noteworthy.
I thought she was like level 12 to 15 or something? I can't remember, but she's a significant challenge against Haley and she had to have taken multiple levels in multiple classes to become a Mystic Theurge.
Also, is it
Low level: 1-8ish
Mid level: 9-14ish
High level: 15-19?