My mother cannot stay motivated or commit to any weightloss program or diet. Any Help?

I love my mom alot! She talks to me about everything. Including her weight problems. She has had a tummy tuck and a reduction in 2005. In 2006 she became pregnant with my baby sister and after that she inserted Mireyna birth control (however you spell it) After that she kept gaining weight over the years. In 2008 she started running and changing her diet. Later that year my stepfather got into a terrible accident and was hospitalized and my mom stopped running and dieting to take care of him. She gained the weight back. And after that, i think the menopause "crazy, moody and unpredictable" side affects got to her. So she started buying diet pills. Stuck to them for 2 weeks and slowly didn't care for them anymore and then got back on them and did the same thing. She then joined a gym membership with a personal trainer...canceled after one week. She joined another private workout club with 7 other women...she was never on time and she showed up late on purpose and quit after 3 weeks. she then got the 2 ball things behind her ears that stimulate her hunger and she wasted ALOT of money on that because she got them taken out and never used them again. She joined Medi Fast weight loss diet program and she spent again TOO MUCH money on buying foods that she wouldn't even eat. And that's only some Other the major things shes done. Shes been on alot of diets and she has asked me to be her motivator and make sure she sticks to them. Ive done that plenty of times and have even tried the mean motivator role. Then she goes and tells other people that im too mean and im no help...she makes excuses for everything. She eats sugared popcorn and drinks carbonated drinks and McDonald's smoothies and says "its only 75 calories, its made of milk, its half water..." What should i do? Im tired of hearing her excuses and im tired of her taking her weight anger out on me.