HI!
This is just a thought, but tell your mom to have a complete blood work-up done, especially checking her hormone levels (including insulin and Thyroid). There are several conditions out there that can cause weightgain or prevent weightloss despite diet and exercise such as hypothyroidism and Polycystic Ovarian Syndrome (PCOS). It's worth looking into anyway. If you can catch them early, you can treat them and start feeling better and even losing weight.