I'm embarrassed and frustrated with my fat sister?

I know this sounds bad, and I am ashamed of being embarrassed of my own sister. I just can't help my feelings. Obviously I never tell her. She must weigh at least 280lb and she's very short. I'm worried about her health, but the thing that most annoys me is her attitude! She's like totally deluded about her fatness! She can say things like "i don't understand why i can't find clothes, and i'm not even that fat"...

Sometimes I'd like to say to her face that she's at least 150 pounds overweight, that's how fat she is! I know this sounds mean, and I'd never do that, but I'm so frustrated. She puts cream in her coffee (cream, not milk!), eats McDonalds and unhealthy things everyday... when we hanged out one day in the city she ate TWO tubes of pringles for snack!!

I feel really helpless and I know she has lots of issues because of her obesity, but she just refuses to take an action. I know she suffers from her weight but she's not trying that hard. I know dieting isn't that easy but you could do something small at least, like have more veggies and put milk instead of cream in your coffee, etc... Am I totally alone with my feelings? Terrible person?
I'm embarrassed and frustrated with my fat sister?
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