Police in France are checking a report of a mystery woman who was seen with missing twin girls in Corsica before their father committed suicide.
Matthias Schepp, 43, threw himself under a train in southern Italy two days later, after writing to his estranged wife on 3 February saying that he had also killed the girls.
However, Irina Lucidi, says she has still not lost hope of finding her children.
She has pleaded for the hunt to continue. Schepp failed to return Livia and Alessia, aged six, to their home in Switzerland on 30 January.
"I am destroyed, desperate, but I must continue to be strong ... but despite everything I have not lost hope and I hope to once again see my girls," a news agency quoted Ms Lucidi as saying.
A witness in Corsica has told police the girls wore pink track-suits and parkas and were eating croissants or chocolate pastries. One had spectacles and a pink and white hat.
"The woman was aged 45-50 with brown hair and was wearing a black three-quarter-length coat and white trousers," she said. "She wasn't from Propriano or I'd have recognised her."
She contacted the police in response to an appeal for witnesses and identified the man as Matthias Schepp immediately from a photograph.