Subsidence and insurance help needed

Hi, I am trying to help a friend to find advice on subsidence and insurance claims please… the story is this:
The house is now about 13 yrs old, it was a new build on unused land by a reputable company, the 10yr insurance has lapsed and the building is now in serious trouble with the lower corner of the block work separating along the joints and rising about 1m50+. The cracks are also visible inside having broken the dry walls too.
My friend has contacted the building insurers and they sent an assessor, it seems his report rejected subsidence due to drought, and it seems they will not act unless the mairie issue a declaration of drought.
Now there also seems to be a clause that the mairie can only declare subsidence if 10 other properties in the town are affected!!.
The insurers “La Poste” seem to be totally unwilling to accept any responsibility on their part unless the mairie act. The house concerned is one of only 3 on a large plot of land, one was a self build, the other was by another reputable local company, and are not showing distress… How can the insurers refuse to act unless the mairie declares a problem… and how can my friend take her case forwards to get the insurers to act, my friend is 72 and worried sick about the problem, all suggestions and advice would be welcome. TIA.