In Gathering Blue, why are all the women who carry rocks waiting for someone else to throw the first?

This section of the novel comes in Chapter Two, as Kira
finds herself surrounded by a gang of women led by Vandara, some of whom had rocks in
their hands. Vandara is clearly against Kira's continuing presence with the people now
that her mother has died. Her disability means that she is unable to contribute to the
people she is a part of in any meaningful way, she argues, and so she should leave or be
killed. However, Kira is able to stop them by referring them to their laws and customs.
In any conflict that could bring death, it must be referred to the Council of Guardians
before anyone is killed. Kira leaves a crucial sentence unfinished, which is finished by
one of the women holding rocks:

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"Yes. The causer-of-death must die." Other voices
repeated it. One by one they released the rocks. One by one each woman chose not to be a
causer-of-death.

Kira is thus
fortunate in remembering this law and being able to cite it. The first woman to throw a
rock could be termed as the "causer-of-death," thus making herself, by law, the person
who should be killed in return.