I watched a few seconds of youtube clips of the X factor and thought Khloe was pretty good. I'm taking into consideration she barely finished high school and has no real skills, other than living her superficial and very insubstantial life in front of the cameras... making kissy faces for lack of any deep thought.
So taking that into consideration, I think she managed very well. She kept a smile on her face, read her cue cards and let Mario do most of the work, which I think was part of the deal for him. That made her look awkward, but it wasn't her fault that she had nothing to do while he spoke.
She was as good as any other inexperienced talking head, IMO.