Elle doesn't respond because, well, she can't. But she does twitch her ears in his direction to let him know she's listening.

She knows he's capable of kindness, she just wasn't sure if it's something he did without a specific motivation to do so. For all his discomfort, helping her was his natural response. He probably debated with himself as whether he should, for various rational and irrational reasons, but he still did it. That means something in Elle's book.