Is it permissible to sell the bags of sugar accumulated by my mother without her knowledge, given that some of them are nearing or have passed their expiration date, and she refuses to donate them?

If the mother is extravagant and wasteful with money, this behavior is not permissible in Islamic law, because it is a type of extravagance, wastefulness, and squandering of money, which Allah has forbidden. First, you should supplicate for her to amend her ways. Then, advise her gently and kindly, and seek help from those who hold influence with her to remind her of the error of her actions. If she persists in her behavior, then her case should be referred to the Sharia court to consider the possibility of placing her under interdiction. However, you are not permitted to dispose of her money without her knowledge. As for what cannot be fed to humans due to spoilage, it can be used to feed animals, for example.