Ye Xinya's cunningness awakened when she did all of that in one fell swoop.
The stuffy feeling in her heart caused by jealousy and insecurity was too much for her to take. How could she not want to get rid of them so badly?
She might not be too different from the other girls since she was also quite materialistic and bound by family rules. However, she liked the guy not as the rich heir Nathan Zuckerberg, but as the liar Jing Mo, and the annoying fake tutor Jiang Li. This was why she felt indignant upon seeing those other girls suddenly taking interest in him just because he was actually a bigshot's son.
They did not see him as he was and had no plan to give him the attention and love he deserved. Why would she let them get near him?
With these in mind, even though she also really had no right, she decided to declare sovereignty upon Jing Mo, to chase away and discourage those planning to use him just so they could reach somewhere higher.