Praise be to Allah.
A woman whose husband dies after doing the marriage contract with her and before consummating the marriage comes under the same rulings as any other wife. Therefore she is entitled to the mahr in full and is entitled to inheritance, and she must observe the ‘iddah, because the Prophet (blessings and peace of Allah be upon him) issued a ruling to that effect. It was narrated from Ibn Mas‘ood (may Allah be pleased with him) that he was asked about a man who married a woman, and did not specify a mahr for her or consummate the marriage with her before he died. He said: She is entitled to a mahr like that of her peers, no more and no less; she must observe ‘iddah; and she is entitled to inheritance. Ma‘qil ibn Sinaan al-Ashja‘i stood up and said: The Messenger of Allah (blessings and peace of Allah be upon him) issued a ruling concerning Birwa‘ bint Waashiq, one of our womenfolk, similar to the ruling that you have issued. And Ibn Mas‘ood rejoiced at that. Narrated by Imam Ahmad and the four; classed as saheeh by at-Tirmidhi and as hasan by a number of other scholars.
End quote from Fataawa al-Lajnah ad-Daa’imah (20/412).
See also the answer to question no. 105462.
Her ‘iddah must be observed for four months and ten days.
Secondly: the woman whose husband dies before consummation of the marriage should observe ‘iddah in her family’s house, not in the house of her husband, because this was the house in which she was living when her husband died.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked:
There is a young woman whose husband died after doing the marriage contract and before consummating the marriage. Where should she observe ‘iddah?
He replied: In her family’s house, because she had not yet moved to the husband’s house.
End quote from Thamaraat at-Tadween (p. 116).
And Allah knows best.