What is the ruling concerning the Hajj of my grandmother who, in a moment of frustration during the crowding of the Hajj, said: "If we had spent our money on a school, it would have been better," and how can she expiate this sin?

The meaning of the phrase depends on the intention of the person who said it. If she meant that waqf (endowment) is better than Hajj in general, then this is incorrect; because Hajj is one of the pillars of Islam and is better than voluntary acts of worship. However, if she had previously performed the obligatory Hajj, and intended that the funds for a supererogatory Hajj would have been better directed towards charitable works such as building schools or hospitals, then her statement has merit and could be correct. But if she intended to express annoyance at the difficulty of Hajj and to belittle the ritual of Hajj, then this is a dangerous statement that could lead to disbelief (kufr), and she must repent and seek forgiveness. If her statement was a result of intense anger that she did not intend, then there is no blame on her, and her Hajj is valid, Allah willing.