This is awful, what a shame Esther was wearing dark/grey clothes. Was she not carrying a flare or GPS? No safety system in place for a solo walker seems unlikely, especially as she's so experienced.
Looking at the Pic de Sauvegarde on google earth, it is relatively sparse up there, no thick forest or anything. I assume she didn't have chance to use the yellow tent to attract attention.
Do we know if she was using the walking route mapped out by google (approx 9 miles), or going straight from A to B along the ridge which forms the country border, which would place her at Sauvegarde? (approx 2 miles)
Google Maps