If I were to give a general estimation as to when i think Maomao gained romantic feelings for Jinshi, it would have been at the end of LN4
Jinshi saves Maomao from her kidnapping, and she returns to working as the Verdigris House's Apothecary. With Jinshi's true status revealed, Maomao assumes she's never going to see him again
She thinks about this a lot, about how she's too low born for someone of his status to ever see her, and how he doesn't even need her help with his injury anyway, because Luoman is at the rear palace now. There's no logical reason for them to ever see each other again. And it itches at her
And so she starts her experiments again, harming herself. There doesn't seem to be a purpose for the concoctions she's making either, as if she's trying to treat something with no obvious cause. Something too deep for the failed medicines to reach
So she goes to cut off her finger. Specifically, her left pinky finger.
Again, there doesn't seem to be a purpose for this behavior at all- until you remember that her mother cut off the tip of her left pinky, out of anguish and rage at Lakan for abandoning her. Fengxian's love for Lakan is the reason her mother harmed her.
Maomao relates that particular finger of her's to romantic love, because of her parent's tragic love story and the trauma it caused her
Maomao knows how stupid love can make even the most intelligent of people, and has consciously and subconsciously avoided it, because she doesn't want to experience that same sort of attachment and hurt. She's heard her parent's story, heard stories of those seeking love at the Verdigris House, how courtesan's speak about love in hushed tones, and how it always ended in pain for everyone involved
But when she thinks she's never going to see Jinshi again, she goes to cut off her left pinky finger, as if on instinct. The finger she associates with romantic love. The same action Fengxian did, when she thought she'd been abandoned by Lakan.
Maomao is doing the exact same thing as her mother, for the exact same reasons.
It's only when Jinshi walks in through the door that Maomao unties her pinky and puts away the knife, and returns to her normal self.
It's one of those things where - I don't think even Maomao understands the reasons behind her actions here. Something was bothering her, something deep, and she went to the only solution she could think of to fix it- cutting off the piece of her that she associates with romantic love- but she stops feeling that subconscious itch as soon as Jinshi comes to see her. As soon as he's back in her life, things are right again, and she stops hurting herself
it's a moment i think about a lot, and it's one of my favorites in the series, because of what it represents for Maomao specifically. it says a lot about her character and how she feels about Jinshi, even if it takes years for those feelings to fully bloom
