Plenty of silicon valley companies resist laws with much larger consequences freely and mostly with impunity.
Some of the same people will be saying uber was a hero for breaking taxi laws around the world (more before it became fashionable to hate uber)
It's not like a Nebraska sheriff can hop over to California or wherever Facebook data centers are and start seizing computers until they found this girl's messages (so much of that process would be absurd).
Just look to Trump to observe what obstructing a court order looks like.
I am not, of course, a corporate lawyer. One would know appropriate procedures to delaying, opposing, or otherwise objecting and appealing an order like this.
But it's Facebook. A half a trillion dollar company can resist an overzealous prosecutor going after a single teenager by just ignoring it and ignoring the consequences of ignoring it. It is approximately equivalent to a billionare not paying a parking meter. Sure, they "have to", but nothing of consequence actually happens if they don't.