A six-year-old girl, named in the press as Kayla, was confirmed as one of the 84 dead by the Swiss authorities on the weekend.
At the time, the whereabouts of Kayla's mother was unknown.
But on Monday it was confirmed that the 31-year-old was also killed when a lorry ploughed through crowds watching fireworks on the Promenade des Anglais in Nice on Thursday night.
Kayla's father and two other children aged eight months and four, with the pair at the time of the attack, remain “hospitalized and shocked” but unhurt, the man's sister told the Tribune de Genève.
The deaths of Kayla and her mother, named by Le Temps as Cristina, have rocked the community in Yverdon-les-Bains, in the canton of Vaud, home to the family.
Many who knew them attended the impromptu memorial outside the church on Pestalozzi square in the city centre on Monday night to lay flowers and candles.
“It's difficult to find the words to explain to her what's happened,” one woman said of her daughter, who used to walk to school with Kayla.
Cristina was of Brazilian origin, reported Le Temps, and many from the town's Brazilian community were among the mourners.
“It's important to us to be here,” one woman, Edila Wagniere, told the Tribune.
“The ordeal that has hit us can hit anyone, when you least expect it, because it's an act of madness that goes against good sense and our religion, any religion,” she said.
In a statement, Yverdon authorities offered their “support and sincere condolences” to the family and said they were taking measures to support the family both in Nice and on their return to Switzerland.
They also thanked the local community for the “many acts of support and solidarity”.
A third victim from Switzerland – a 54-year-old woman from Ticino – was the first to be confirmed killed in the attack.