But Lily was not easily disconcerted; competition put her on her mettle, and she reflected that Selden’s coming, if it did not declare him to be still in Mrs. Dorset’s toils, showed him to be so completely free from them that he was not afraid of her proximity.
There are no more uses of "mettle" in the book.
Show samples from other sources
The Trials are a test of my mettle.
Sabaa Tahir -- An Ember in the Ashes
But I will say, too, that for every man who showed no fear or hesitance, there were three or four or five others whose mettle was as unashamedly wan and mortal as yours or mine.