What is the ruling on giving money from a mother afflicted with Alzheimer's to buy food for her son?

If a mother is of unsound mind and unable to manage her own wealth, she is to be interdicted from it, by consensus of scholars. Her guardian must preserve her wealth and manage it in a way that benefits her. It is not permissible for him to donate from her wealth or to dispose of it in a manner that does not benefit her. It is not permissible for children to pay for their food from the mother's wealth, and restitution is required. The guardian may spend on the mother and those whose maintenance is obligatory upon her, in a reasonable manner, without extravagance or parsimony.