Jia Baoyu named Lin Daiyu Pinpin, why only Baochai called her a frown?
In A Dream of Red Mansions, Lin Daiyu should be older than Sanchun's sisters, so there is no saying that young age is older. Baochai is old, and it is reasonable to call her by her first name. And it's hard to say whether it's true or not, and elders may not take it seriously, and it may not spread among sisters. Moreover, Daiyu and Baochai were originally nicknames, and the elders called them very kind. Although Baoyu gave Daiyu a name, it was too outrageous to call her Miss in ancient times. People nearby didn't get a chance to call her, but Baochai did.
"Pinpin" is taken from Baoyu (Cao Xueqin) who praised the beauty of Daiyu, implying that Xue Baochai's brother Xue Pan loves Lin Daiyu, and his concubine Xiang Ling is related to "learning from the East". Xue Pan married because she heard that Xia's daughter could read and write poems, and she was beautiful, so she insisted on marrying. (Naturally, I love Daiyu, and I can't get it, but I still want to "share the same paragraph". Unexpectedly, Xia Jingui is not what Xue Pan imagined).
So the overlapping of "products" means "two". Since it is a meaningful name, the natural author will not always call people Daiyu Pinpin, Brow, Brow Sister, Brow Girl, Brow Girl and so on. Then arranging Baochai to call each other is naturally the author's interest, and this name is only related to the Xue family.