It seems she did it because she want to show Jin that she'll be fine by herself, without Jin to help her, so he can go live with human community without worrying about her.
But yeah, things esculate very quick next chapter....
Edit: fix link
Calm down. She's just middle schooler who don't interested in love (yet). She don't even know the feeling of what to be in love, so she just find the nearest feeling of having someone special for now. Give her sometime, untill she figure it out.
My interest in this arc is decreasing since it's been drag on and on with many hiatus for a long time and now I feel nothing but "it's finally end, hm?".
Hope Sword&Shield not meet the same fate as this arc.