That unspoken rule was broken this week when the nine American citizens from the Mormon community were ambushed and killed. So too was another drug war maxim: that women and children are not to be touched.
"Until now, I loved living here," said Miller, who grew up in a similar Mormon community just over the mountains in Chihuahua state.
She said her family has long had close relationships with the locals, who work in Mormon homes and on their pecan and pomegranate farms. When Miller's son died last year in a small plane crash, more than 1,000 people showed up to the funeral, she said, and locals hired mariachis to play.
Losing her son had prepped her and the rest of the family to deal with Monday's loss, she said. "If that hadn't happened to us we never could have survived this."
Her son Howard moved down from the U.S. with his wife, Rhonita LeBaron, and their children this year, in part to help out after his brother's death.
LeBaron was excited about living in Mexico, where life was more relaxed than in the U.S., and where their seven kids could roam.
"She was the perfect mother," said Miller.
On Monday, LeBaron joined a caravan of women and kids who were leaving town to drive to the border to pick up Howard, who was flying back from North Dakota, where he worked in the oil business. Traveling together, the women thought, would protect them from the dangers of driving desolate roads through drug cartel country.
Shortly after leaving, LeBaron got a flat tire. The caravan returned home and LeBaron asked Miller: "Do you think that's a sign that I shouldn't leave here?" But she left anyway, switching vehicles and heading out again in Miller's 2011 Suburban.
When her son went to check on the broken-down vehicle, he found the burned-out Suburban. Up the road, members of the Mormon community would discover the two other vehicles that had been part of the caravan riddled with bullets and strewn with bodies.