Her ability to do that is a mystery.  More on that in a moment. 

Now Lara, if she was around at the time, would be actively trying to reject the Kaos energy.  She doesn't want to absorb any of it.

Liu Xi might be worried that she feels like she's so close to the source of the Kaos energy.

As I mentioned above, her ability to do that is a mystery.  Nobody is sure whether she's actually psychic or if she's just very adept at putting things together, or if she's just very, very lucky.

Case in point:  Maybe she does sense the dark energy.  Or maybe she just realizes that things around her seem to be changing under the influence of dark magic and knows that means bad things will happen soon.  Maybe she senses that Tom Black is the cause.  Or maybe she just remembers that the weird behavior around her began around the time he went to visit his storage vault, and that his family has a history of tampering with that kind of dark magic.

That's not an exact case but it illustrates where the mystery comes from.  Until Chiaki herself speaks up on the subject nobody seems to be able to come up with the truth.  The point is she might actually be psychic, or she may just be very perceptive and attuned to the world around her.  If she is psychic she would definitely get a headache, she either wouldn't tell anyone or she'd understate it (nobody will pay attention if she takes a nap to get rid of a headache) so that would just add to the mystery.

I'm sure one of these days Yuki intends to solve that mystery when she's less busy.  :)