I have had people say things about my weight and please believe me, all it has done is alienate me from them (my choice). I think people think they are being some kind of helpful when they make their backhanded comments about weight but really, it made me go home and eat more.
You said you "heard" she's wearing whatever size clothes. How does someone "hear" that? No wonder people like me cut every tag out of my clothes before I ever went to anyone's house just in case someone wanted to know how really big I was. And I thought I was just paranoid.
Just be a good sister to her and accept each other for what you are. That doesn't mean I don't want her to get healthy. But you and your mom (or anyone else) aren't allowed to tell her what to do.
I almost wish I could be a mean person when people say things about my weight. It's like people think if they don't have a weight problem, then they are perfect and can say whatever they want to a larger person.
I haven't seen hardly anyone in my or my husband's family since I have lost 137lbs. If they couldn't be nice to me at 328lbs, then I don't need them at 191lbs.
Please tread lightly with your sister. Life is too short to try and change other people. And I say that directly from my heart. Enjoy your sister, I wish I had mine in my life.