The angle that leaps to mind is some property flipper saw the place listed and hired some shady workmen to tear the driveway out knowing it would fuck up any pending contracts, and he's hoping the owner will be desperate enough to take whatever lowball offer he swoops in with.
But that seems like a pretty risky scheme, unless he's also planning on not paying whoever he hired to bulldoze the driveway. And I guess before you get the driveway replaced you ought to make double damn sure you're not hiring the same motherfucker who ripped it out.
You're correct in that there's no way you're going to be able to haul away a concrete slab that big and keep it in one piece to be reused elsewhere. And even then, for what? You have an application that needs a slab the exact size and shape of this lady's driveway?
Another option, she's buying a new house down the road, and selling this one to pay for it.
If the person who did this wanted the other house but lost out on the bid, this is a fairly low-cost way of fucking up that deal. And if the deal still goes through, then it's just a costly act of petty revenge.
concrete can be crushed and reused as part of the agregate mix, which is probably exactly what happened to it. waste not want not, right?
In any case, if it wasn't a scumbag flipper, then it was probably the contractors using the pressure of the listing to force her to accept the first not-actually-low-ball offer that comes along. (and then all the sundry other bullshit contractors pull to inflate the price of the job)