mccombs was born in kaiapoi, north canterbury, new zealand. she was one of the nine children of alice and daniel henderson. the family spent some years living in ashburton, but in about 1882 the family moved to christchurch. a passion for activism was embedded in her family, as some of her siblings were notable activists themselves. two of mccombs' sisters, stella henderson and christina kirk henderson, were both in the public eye; stella writing for a prominent new zealand newspaper, and christina advocating for the suffrage movement.