Even the loss of her jewels did not disturb the lady's equanimity.

Temper : a person's state of mind seen in terms of their being angry or calm.
Composure : the state or feeling of being calm and in control of oneself.
Affability : the quality of being affable; geniality.
Humour : the quality of being amusing or comic, especially as expressed in literature or speech.
Equanimity : calmness and composure, especially in a difficult situation.

Synonym of Equanimity is Composure