In Frontier Wolf, what is the importance of the swordsmith's daughter?

Question

In Rosemary Sutcliff's novel Frontier Wolf, tensions rise between the Romans and the Votadini after Connla, younger brother of the Votadini chieftain Cunorix, steals the Roman Praepositus's horse. Cunorix is very angry at his brother, but Connla is unrepentant:

"The Chieftain said he wished to breed [his mare] from the horse. I only did the thing to please the Chieftain my brother."

Standing on the threshold of his Hall, Cunorix looked back at him with no trace of answering laughter. "Did you so, little brother? It is in my mind that you did it because the Praepositus refused and you do not like the Praepositus, and also because you thought it would be a fine sport."

Connla swaggered a little, his hands on his hips and the laughter dancing like summer lightning behind his eyes. Several of the tribe who chanced to be about their business nearby had drawn closer; among them two or three girls from their looms or their grinding querns, and among the girls one who was red-headed as himself, Teleri the swordsmith's daughter.

At this point, a Roman delegation arrives, carefully asking after the horse without making any accusations. Cunorix replies, without making any admissions, that the Votadini have indeed "found" the horse, and he tells Connla to fetch him.

Connla stood a long moment quite unmoving. He had gone an odd pearly white, his eyes suddenly very dark, fixed on his brother's. Then he flung around and strode away.

He brings the horse, and the Romans ride away. The incident appears to have been peacefully resolved. But then:

The swordsmith's red-haired daughter who had come out again with a knot of other girls to watch gave a crow of high mocking laughter. Connla swung round on her, but what she saw in his face made her laugh the more. "So much for your horse-raiding, my bonnie lad!" she said, and turned with a flick of her saffron skirts, and walked away.

...

If the red-haired girl had not laughed, much of what happened after might never have happened at all.

What happens afterward is that Connla steals the horse again. He is captured and killed, and the Romans and Votadini end up on opposite sides of a war in which many more characters die.

The narrative implies that the red-haired girl is to some degree the cause of these events. Connla wants to impress her, and her mockery goads him into his disastrous choice. Other than that, the girl is not an important character; she appears only in this one scene. This raises the question, why include her at all? Connla is certainly proud and reckless enough to have decided on his own to steal the Praepositus's horse a second time. What narrative purpose is served by the swordsmith's daughter?

Answer 1

the girl is not an important character

I think this is the point. For lack of a better term, this strikes me as a "for want of a nail" moment.

For want of a nail, the shoe was lost.
For want of a shoe, the horse was lost.
For want of a horse, the rider was lost.
For want of a rider, the message was lost.
For want of a message, the battle was lost.
For want of a battle, the kingdom was lost.

The idea that monumental consequences can flow from insignificant and accidental causes is a fascinating one, and always has been. It speaks to our ultimate inability, as individuals, to really control the world around us (hard as we try) or predict the full consequences of our actions. It makes us think about the fickleness of fate. It invites us to ask "what if".

If Connla had simply stolen the horse a second time, without any external prompting, it would give the impression that the war was inevitable: he was determined to tick off the Romans, and it was only to be expected that the Romans would retaliate. The reader would feel that the war was "fair", in a certain sense. But to frame the war as the consequence of a woman laughing—a woman who couldn't have possibly foreseen what would come of her actions—makes the war feel more avoidable and unnecessary, which increases our sympathy for the characters who are caught up in it.

(Disclaimer: I have not read the book, so my answer is based solely on the information you provided and some educated guesswork.)