Remember what the masters said:
"In you we saw a wound in the force..." = Kavar
"in you we saw the end of the force." = Zez-Kai Ell
"You are a threat to living creatures, and all who feel the force = Vrook
She used the exile to try to end the force (You are a threat to living creatures, and all who feel the force) and all its teachings.
Kreia does not like being "used" by the force, to obey its will but the exile was an exception. The exile cut himself off from it (to turn away from its will). Then the question comes, why is she using it?
Well she explains:
"I use it, as I'd use a potion and in the hopes of understanding it - I'll learn the way to kill it".
She used the exile too, using "his/her" death so the Sith would believe they had won - and turn against each other (Sion and Nihilus). She wanted to end them because they wounded her.
How do you end the force? By killing all the force users of course, if no one understands the force then it cannot "control" anyone any longer. That was her goal!
...I know, she's a witch.