Thanks, NatJM. This person didn't have any works and the story would be simply based on her life. If the story isn't going to defame her, do I still need a permission?
The legal maxim is that one cannot defame the dead. I can write a movie about Edison and pretty much say anything I want about him without worrying about it.
A defamation lawsuit has to be brought by the person who has been defamed (or by a legal representative).
I think that the answer to your question lies in the question itself.
Who in the world would you go to to get permission?
If the person in question is dead, and has left no living descendants, it would seem to me that no one remains who has any valid interest (in a legal sense) in her "life rights."
I suppose -- and this is advice that I always give -- a newsgroup is never a place that one should go for legal advice. That's what lawyers are for and before you make the commitment to devote all of the time and effort to writing an entire screenplay, it might actually be worth the time to talk to a lawyer who knows something about intellectual property rights and get this issue clear.
Even if you have the right to do it, it will no doubt come up again when and if you sell it, since, if it is based on a real story, the contract itself will have to be phrased a little bit differently.
NMS