My own personal opinion is that the Passat struck the Megane at speed, lost control ( airbags deployed?) and then wobbled, skidded to a halt further up the road on the wrong side, with the passenger side facing oncoming traffic. The Corolla then came around the corner at a 'normal' speed and colided side on with the Passat, pushing it back down the road and into the ditch, with the Corolla landing on top of the Passat.
If the lady in the Megane was ok I don't think the Passat could have been travelling at an excessive speed when it hit her. Going from your post Colin I think it's possible that the Passat was doing a normal speed but simply lost control of the car due to the number of people in it. All speculation.