Your mother must feel so lucky to have a wonderful daughter as yourself. Poor body image effects millions and millions of people, so let your mom know that she isn't alone with her feelings. The problem though isn't how she looks on the outside, it's hers and the millions of peoples mentality that needs to change. Not stress so much about how we look, but focus more on what's inside, and this is so much easier said than done. Your mom and myself and the rest of the world needs to retrain our thoughts and re-evaluate what is more important in life. After all, in the end all there is left is what's on the inside once looks start to fade.
So Mom please don't feel so low about yourself, it should make you feel good to have raised such a sweet and caring daughter who's willing to do anything for your happiness! ~Take Care and Best Wishes~