[incorrupts]

Originally Posted by Levy

That was true untill Lelouch wear his 'Emperor' mask. The tyranny he established, and what he did immediatly after their encounter in Turn22 is something that conflicts openly with what Karen believes in. Is that the part I can't see her approving - this, along with Lelouch letting himself be killed.

Their encounter in #22, was before Lelouch committed the "atrocities" he had in mind in order for the ZR to succeed.
After that, then yes Kallen chose to oppose him even if she loved him. I do not get which part you do not get.