Teachings from a previous era have brainwashed your mother and many others. At that time, popular folklore emphasized a daily elimination to cleanse toxic substances from the body. It can be normal not to have a movement for three days. Hardness of stool and excessive straining to eliminate it are better criteria of constipation than is frequency of movements. If your mother increases the amount of fiber in her diet, it will produce the desired effect.
People ought to invest a small amount of money in a pamphlet that lists fiber content of foods.
They are in bookstores, and I have seen them in supermarkets. I don't know if your mother's weakness and tiredness stem from laxative use. It's a question that begs for an answer. Something more sinister might be occurring. When I exert myself, a large lump appears between my breastbone and navel.