I think I might have found Claudette Souchon, I've come across someone of exactly the right age, in a region 50 odd miles to the NNW of the Camargue (Arles), and about 80 miles east of Rodez. Rodez is in fact 100 miles NW of the Camargue. She went to both primary and secondary school at this place, and someone by the same name is still, or was very recently, associated with the place. And I hope it's her because she seems to doing quite nicely. Her schooling is recorded in the primary between 1955 and 1959, secondary from 1959 to 1964, corresponding with someone born in 1947 having started aged 8, and left at 17.
The Express seems to be the first source and it says she was taking a two day tour of her property, big farm then. Is that possible in Southern France? The magazine article says she went out only for the morning, but then why take two horses? Either way are any of these details likely to be accurate or relevant? We have no clear evidence what happened to the dead horse or what relationship it may have to the rest of the events. By the time they got into the paper the description of the injuries are at least third hand, two pairs of which were probably attached to journalists.
If her clothes were identified and actually found in a glade that was literally burnt out they must have been put there after the fire. I think it's more likely, if there's any truth in this part at all, they were found near a fire site. As Enolagaia says that sounds like she was drying them by the fire, but then she'd have been unlikely to leave them unless they caught fire accidentally. But then without the idea of a naked vulnerable woman I doubt a rag like the Express would have been interested. I think we might consider taking this detail with a pinch of salt. There's also the horrible idea that her clothes were taken from her, if this is the case we're treating something horrific as something intriguing, albeit not deliberately.
Dinard is given as the Police Chief for the area, but which area? The Camargue, the area where I've found the name, and Rodez are all in different administrative regions. It's doubtlessly possible to spend days wandering lost on the Camargue, but it's impossible to move between any of the three areas above without crossing multiple roads, probably hundreds. Yes there are probably more roads there now than 1978 but go to Google maps and move the little man between Arles and Rodez and watch everything turn blue. That she could have stayed lost covering such a long distance seems impossible. Even allowing for exacerbating factors such as exhaustion, delirium, panic, disorientation etc.
The article rules out assault, thankfully, but it's hardly quality journalism, and a lack of evidence of assault doesn't rule out abduction. That'd be the most obvious explanation if she was found anything like the distance stated from her starting point. But then there's the dog, which undermines the likelihood.
Either way this is not mysterious. The newspaper the article appeared in was and still is a sordid little rag. That it starts off with attractive Claudette Sochon, 31, tells you what sort of article you're reading. Salacious details like horrifically injured horses, naked women, and melodramatic French police officers are given clearly, but we're a bit light on facts such locations, timeline, or a source.
There are two obvious options; she got lost and was found suffering from exposure, or was abducted and was found suffering from worse. If she was just lost she can't have got anything like as far as was reported. That there was never a widely circulated resolution to this is probably just because any further coverage was in French and the story was never carried on by the Express' Paris correspondent.