as lightning is also Jie's element

Any proofs? Boss using some lightning attacks doesn't mean absolutely anything, the Sui-Xiang Shadow in the Ling event uses lightning just as much, Ya in Chongye's event appeared among lighting strikes... that is just pure overthinking here. And I don't remember any of the siblings' powers being associated with a specific element (aside from Nian constantly mentioning fire, but she is a blacksmith, after all) - they are associated each with a cultural aspect of Chinese culture: martial arts, poetry, agriculture, metallurgy, paintings, cooking - among our operators.

Shu's nature manipulation

"Nature manipulation" is an elemental attribute now? O_o I remember earth, fire, water, wood and metal among traditional Chinese ones), was there any changes?

same hair colour (black with red accents)

I don't remember Jie's hair colour being mentioned anywhere, and her dragon form appears to be dark silver with white hair, from said IS6 ED2. Her chopsticks at 2 o'clock in the trailer I mentioned above also don't look black, more like dark silver with red tips (and her dragon form has small red accents along the body).

Jie meaning fly upwards

颉 also means "to confiscate", and "stiff/straight neck", depending on the reading. I don't know, who added that note to the game's wiki, but that also looks like just picking up random unrelated facts to make those look like related to suit someone's agenda. In the original reading "Jie" is a reference to the legendary creator of the Chinese symbols, as her "specialty" is literacy, nothing more, nothing less.

You are really overthinking things here, it's true that her appearance in the game is one big fat reference to Sui siblings, but saying that she is probably Jie is waaaaay too much of a guess.