....okay 
i have an idea
a familiar 
a familiar would be an animal that would lend more power to the witch
the price is that the two are linked
if you catch the familiar you catch the witch.
its like a piece of the soul is there
only difference is if you kill a familiar it does not kill a witch but it does hurt them significantly even weakens their abilities to lower then what they started with

thoughts?

edit: also...what about spell books? 
i think with this one, the witch would have their power that does not need spells
and then can do other things with spell books
those who have gotten really good might be able to memorize them and think of the spell hard enough to do it...those inexperienced would need to say it out loud somehow 

thoughts on this as well?