Hazrat Aamir Sha'bi (may Allah have mercy on him) said: If someone wrote a letter to his wife: "Begin your 'iddah," and the wife passed away before the letter reached her, then if the 'iddah was not completed, she will share in the inheritance, otherwise not.
Hadith Referenceسنن سعید بن منصور / كتاب الطلاق / 2366