Is it permissible in Islamic law for a single, disabled woman who was left alone after her mother's death to spend the martyr's son grant that reached her mother after her death on herself to meet her needs?

The original principle regarding the grant money is that it belongs to all heirs. However, if the brothers fall short in providing for the questioner's maintenance, then she has the right to take from the money an amount equal to the maintenance they are obligated to provide her. This is known as the issue of "seizing one's right." It is permissible for someone who has a right against another, and is unable to obtain it from them, and then seizes something from their property, to take from it an amount equal to their right, especially if the cause of the right is clear, such as the maintenance of a wife or relatives. The evidence for this is the hadith of Aisha (may Allah be pleased with her) that Hind bint Utbah took from Abu Sufyan's money without his knowledge, and the Prophet (peace be upon him) permitted her to do so. This has been supported by Ibn al-Qayyim and Sheikh Ibn Uthaymeen.