My mom and her weight? Please help? Doctor or person from experience?

My mom is always talking about how she is not happy with her body. My mom used to be very tiny and skinny like I am now and she gets very sad looking at pictures of when she was that way. However, my mom eats the way my sisters and I do. It's not the healthiest food. She doesn't work out everyday and she does exercises that actually sort if build muscles like with weights and crunches and stuff. My mom is 5'2 and is 47 years old. She says she has a thyroid issue...She always uses the fact that after she had child number 3 her metabolism hit a brick wall. But the truth is, after she had my little sister she bounced back and still was skinny. I want to know, how can I tell my mom that she needs to eat healthier and do more workouts made for what she wants to do if she wants a healthy looking body. I don't want to offend her. My mom gets offended easily, but I hate when she tells me she isn't happy with her body but doesn't really make an effort to change it. Please help? It would mean so much to me?