How do I get my mom to get serious about her weight?

well just talk to her about it. try to motivate her ask her to come and excercise with you.

Plan to talk to her while out together. Come up with a list of fun activities that you can do together, like joining a bowling league, taking walks, or joining a gym. That way, she can see it as a fun plan, rather than take offense. I am not saying she is that type of person, but my mother was easily offended, but not about weight as she was as thin as a stick her whole life. But, she wouldn't accept any remarks she deemed rude and the bar was set very low. If you still live in the home, buy the groceries and do the cooking. That way, she will see it as a nice gesture, rather than be offended. Again, I don't know if she is so easily offended, but just to be on the safe side. The other option would be to discuss with your father. But, she could get insulted if he broaches the subject. It is sort of a sticky situation. Maybe, activities would be best if you are close geographically.