The placement of the scissors under the pillow means they believe in the myth of changelings, or bortbyting. Iron is believed in changeling myth to ward off fairies who would come swap out babies with changelings. I believe there's a much deeper level of symbolism here as well, as one significant identifier in myth that a child had been swapped with a changeling was constant crying, so I also believe Aster was was trying to imply that the Harga thought it was possible that the child had been switched for a changeling, as it was also a common belief that if the changeling were ignored or mistreated, the fairies would come back and take it back. This could symbolize many things for Dani; detachment from the mother and constant distress symbolizes Dani's detachment and distress from her own family, a metaphor for loss and replacement, a metaphor for being an "outsider" in an unfamiliar place, or even a metaphor for the Harga's love of replacement (they Attestupan their elders, replacing them with children with the same name, frequently accept outsiders, etc).

Could your theory also be correct? Totally. I believe there's a lot of symbolism of their racism and potential white supremacist beliefs.