I don't think that Kimura is unaware of Hiyama's feelings for her, she might not fully understand them yet but on some level she can definitely tell that Hiyama is interested in her. This has actually been a really wonderful manga so far, and is very different from the pre-serialization version, which I'm super happy for. I'm really hopeful for their relationship and I love the ways that Kimura is trying to change and become more confident.
I don't see a lot of people talking about this but the fact that right before she bumps into Hiyama, Kimura says "I want to become someone that I can love" and then after seeing how Hiyama's heart was racing so much that she fainted she said "It's strange, but I feel a little better than I did this morning" and thanks Tomoe for the beauty make over. I see this as her gaining a little confidence by understanding Hiyama's feelings for her, even if only a little bit.