She might, but clearly she's weighed that decision (Pun intended) and–as a rational human being with agency–decided the value of losing 100lbs is not worth it.

That fine. We're all adults, we can make those choices; and it's wrong to shame somebody into making a different choice — the choice you might feel is right for her.

Reframing the argument: Clearly a multilingual speaking person is better than a monolingual speaker; they can participate better in the global economy & contribute to a broader society. But learning other languages takes effort, time, and work.

I might say that if you don't learn other languages, you are a bad, lazy, incompetent person; a lesser person than I. Clearly you should be shamed into making the right choice about languages, my choice about languages.

Surely you can see that in a free society this is unethical. You've weighed the choice of learning other languages, and decided against it. It's not my place to tell you my choice is right and yours is wrong; that's what you're there for — to make your own choices.