My grandmother died in the house and was left for twenty-four hours in the same clothing in which she died without being washed or shrouded. On the following day, before she was washed, her body became foul-smelling so much that no one liked to wash her, save her young daughter who washed and shrouded her dead body. Her face started to turn green or even blue.
My question is: Does this go back only to the delay of burial or to something else? She has never left prayer or fasting for even a day. I like to rest assured about this issue.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

The delay in preparing and burying this deceased Muslim till her body changed in color and smell is unlawful under Sharee‘ah. This is because, unless the cause of delay is beyond control, this violates the sanctity of a Muslim whom Allaah The Almighty Honored and of whom He enjoined the burial. It disagrees with the command of the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, to hasten in preparing and burying the deceased and gives no consideration to the observation of the rights of parents and being good to them after their death. This is in regards to the delay not being caused by something beyond your control.

The change in color of the face seems to be caused by the change of smell which took place as a result of the delay and nothing more. Because this woman used to perform her prayers, fasting and obligatory duties as it should be, she will find nothing but good, Allaah Willing.

It is due on a Muslim to conceal what he sees of the states of the deceased which people may think to be a sign of evil. It is narrated on the authority of Abu Raafi' : “He who washes the deceased and conceals what he sees of his states, Allaah forgives for him forty major sins.” [At-Tabaraani: Marfoo'] Commenting on it, Al-Haythami said: “Its narrators are the men of Saheeh (Hadeeths).” According to the narration of Al-Haakim in Al-Mustadrak, “… Allaah Forgives him forty times.” He mentions that it meets the same conditions stipulated by Muslim .

Allaah Knows best.