One common theme is the clash of different cultures. Harry Potter comes from a world of magic with wizards, spells, and Hogwarts, while Edward Cullen is from the world of vampires in Twilight. The fanfictions often explore how these two very different cultures interact.
Love against all odds is also a big theme. Since they are from different worlds, their relationship is not easy. There are often obstacles like the differences in their nature (human - vampire, wizard - vampire) and the expectations of their respective communities. But they still manage to fall in love, and this love is portrayed as something very strong and deep.
Another theme is self - discovery. Fem Harry Potter, in these fanfictions, often discovers new aspects of herself when she is in the company of Edward Cullen. For example, she might find new ways to use her magic or she might learn more about her own emotions and desires. Similarly, Edward Cullen might also learn more about his own humanity or lack thereof through his relationship with fem Harry Potter.
A practical answer is Chapter 120, because it turns the idea into a concrete scene. The chapter opens with Facing the sudden and somewhat strange request from Jiang Li, Director Sun..., adds pressure through Netizen: Wen Jiaojiao had been acting for years without much fame, but now..., and ends on.
Chapter 97 is the strongest chapter-level answer because it starts from Suddenly, Jiang Li's livestream room was packed with people, and the... and follows through on And you believe what she says?.
The best chapter pointer here is Chapter 84, "Is it Just About Having Hands?". It opens with When the villagers tasted his curry beef one by one, their faces revealed... and closes on Why am I tasting sand in my mouth?" Wen Jiaojiao's bravado gradually....
The best chapter pointer here is Chapter 106, "The Beginning of the Butterfly Effect". It opens with Thinking of this, He Yun nodded with a hint of anticipation. and closes on Jiang Li's fingers lingered over the three copper coins, her clear voice....
The best chapter pointer here is Chapter 85, "They must have been bought off by Jiang Li!". It opens with Facing everyone's skepticism and curiosity, Jiang Li explained fluently:... and closes on This fresh and vibrant flavor blended perfectly..
If you want the clearest chapter reference, go to Chapter 114. Early on, As time passed, the number of viewers in the live broadcast gradually...; later, the chapter leans on After a whole day of trending searches yesterday, the popularity of....
The best chapter pointer here is Chapter 80, "Princess Wen, Your Lunch is Escaping!". It opens with Jiang Yan and Wen Jiaojiao, one so smug he was almost ascending to the... and closes on arrogant princess with Princess Disease, I'm totally for it, fam.] [Hahaha....
If you want the clearest chapter reference, go to Chapter 86. Early on, After over an hour of fuss, it was finally time to eat.; later, the chapter leans on Qi Tianyu, starving, crazily scooped up his curry rice into his mouth..
If you want the clearest chapter reference, go to Chapter 104. Early on, Zhao Lang let out a light chuckle, "Young Master Jiang, don't be nervous,...; later, the chapter leans on You're Daddy's guests, how could I possibly come to settle scores with....
If you want the clearest chapter reference, go to Chapter 126. Early on, Wen Jiaojiao initially wanted to cause trouble.; later, the chapter leans on But when her gaze swept around and landed on Jiang Li, who was standing at....