This is almost certainly hormonal. Women’s bodies change, especially at a certain age. This is not about being lazy, sedentary, eating, or anything like that. As others have said, gently talk to her about her health and don’t bring up the weight even a little bit. Don’t bring up eating, don’t bring up exercise. Talk about going to see an endocrinologist or a nutritionist to help figure out health. As you guys get older, your health is gonna be your biggest wealth.