Food waste is a real concern facing our planet. Just think of all the resources that go into producing those wasted pounds of ground beef!
In this case, you need to be the parent and enforce some rules around food budget and quantities. There's no reason to double recipes when no one is eating leftovers - that's nuts

And while you're at it, I would encourage your daughter to educate herself about food waste and the impact it has globally.
As for her friend's family, their behavior is just some embarrassing, bougie flex. My ILs are self-made wealthy and they behave in the same obnoxious manner, constantly wasting food and refusing to eat any leftovers, as if that choice somehow makes them superior. One Thanksgiving I watched them struggle to stuff a still warm turkey into a garbage bag head for the trash. Eventually a 3rd person had to step in to get the job done and then they all stood there beaming with foolish pride about their actions. Truly vile and disgusting behavior!