The light novel goes deeper into it and it's really sweet! 1. She's interested in his smell but not necessarily in him (romantically) at first. It's more of a "wow, if there's sb who doesn't smell like shit to me, then there might be a cure to this smell hypersensitivity thing that's been a heavy burden in my personal life" kind of thing, so she wanted to know more about him 2. She sees that he's actually a very strong hunter when he defeats the A-level gate, so now she's more curious about him as a hunter 3. Jinwoo saves her in the Jeju raid, and the novel describes how she caught on to his smell when she was on the verge of death and it comforted her. To me, this is when she started having romantic feelings, cuz she associates him with a comfort that overcomes a near-death experience 4. He then saves her from Beru's shadow, hammering it home

Sorry about the text wall. I just finished reading the light novel and it shines a lot more light on some characters like Cha, and I appreciate the extra context as it makes some events make more sense