Sonja is not oblivious to Katniss's reactions to the incrementally nearing fog--she doesn't mother quite as she might, say, Ilde, because she doesn't know Katniss and they're two different people, but she notices. She's attuned to people's moods in general, but she pays more mind to those she already knew, and frankly, Katniss already strikes her as someone she could have met at home, so she's more inclined to...care.

So, of course she doesn't bring it up or ask if she's all right or anything like that. Instead, she ambles over up on deck.

"You're good with that bow, yeah?" And by 'good', Sonja's tone suggests not just 'better than average, but 'insanely competent'. It's a knack, that inflection of hers.