What constellation is the big girl Shen Siyi?

It's Sagittarius

According to the description in The Great Girl, Shen Siyi is a Sagittarius. She always holds a joking attitude towards love, which shows that she lacks the courage to affirm love. Sagittarius is like this. It is too difficult for them to give up their freedom and give their lovers a sense of security. Moreover, they pursue freedom and do their best to get married.

The Great Girl is an urban youth love drama directed by Ding Jieru and Qiu Shengbin in 2020 and starring whitehairpin, Gina and Zhang Zuke. The play tells the story of the successful transformation of a pair of sister flowers with a publication "Life Home".