In this case mother knows best, and it won't help to call her grumpy (did you duck when you said that?) The moisture in the house from leaks has probably given rise to a bumper crop of molds and mildew. There are individual that are more sensitive to this than others and would be affected just as you MIL describes. As the house dries out, your problem should be reduced. Meanwhile, try to find the areas that have been affected by excess moisture, and treat them with a fungicide (disinfectant). You should work to get the situation under control by getting things as dry as possible and treating affected areas. This problem can affect the value of your home and the health of those that live in it. Who knows, maybe if you are good, the MIL will feel good enought to cook for you, but not if she hears you called her grumpy.