The reason a lot of peeps cannot act their age when talking to toxic parents is because their brains automatically slip into their "hurt inner child" mode: a set of perception, automatic behaviors, and undigested emotions left behind by all the parent interactions throughout their childhood. With that in mind, big respect to Chengxin for actually drawing and enforcing a boundary, even at a great emotional cost.
Also, I have to wonder where on Earth this story is taking place? Chengxin's mother asks for yuan, mentions having USD, and then Chengxin's date tranfers yen to her. We've already seen in earlier strips that geography is more of a vibe than a physical space in this comic, but I wonder whether this is part of the author's concept?