Interestingly that's exactly what I used for a recent encounter. For some reason I even arrived at a CR of 12 (I assumed the levels would be associated). Actually, I didn't find her 'woefully underpowered'. I mostly chose buff & touch spells for her and used a mwk/+1 stunning surge quarterstaff to good effect. I selected power attack and brutal strike as additional feats.
I'm not sure if posting the whole statblock would be fine - assuming you were interested?
