This is a stretch on my part, but it's possible that Teresa's moment of ease coincides
with the moment when Nostromo sinks the lighter. Allegorically and symbolically,
that action stands for the People severing their fidelity to the larger society,
and though it will take Nostromo the character somewhat longer to get there, it
is exactly what Teresa wanted of him. Tellingly, however, her ease is short-lived.
With the People's defection that she urged, society is reduced to helpless ignorance
and reactive violence, an example of which will immediately do her in.