After understanding what her opponent was plotting, Violet hadn't planned on immediately intervening or sending a warning to deter them.
She knew that doing so would be futile.
At that moment, she conceived a better plan to deal with them, although it carried some risk.
Yet, risk also implied rewards. If one constantly recoils in cowardice, lacking the courage to face these risks, they will undoubtedly accomplish nothing, exhausting a tremendous amount of resources in the process.
The crux of the issue was that Violet couldn't afford such a heavy toll on resources.
She didn't have the energy to engage in such meaningless, covert skirmishes with these villains. It was simply a waste of time.
So, she had to come up with a better approach to permanently resolve this predicament.
If she were to directly warn these miscreants, it would only disclose that her covert operations were inadequate, resulting in the leakage of important secrets.