My last message posted automatically. Oh, well...
The place you named in your message : « Val d'ouis », does not exist. Perhaps you mean the département of Val d'Oise ??? I can only guess.
However, if you only have the name of the département, you must get the name of the CITY (in French = « commune ») where she died.
Once you have the name of the city, you can order her death certificate online here (it is free) :https://www.acte-etat-civil.fr/DemandeActe/Accueil.do
The death certificate will have the names of all of her previous husbands, if any, her parents, and it may have the names and addresses of witnesses - who you could research in telephone directories.
Good luck to you !
Bonne quête !