As a side note, while I still believe it's the responsibility of the ass-hat who lost the load in the first place, by law, if you're following so close you can't stop in an emergency, that makes it YOUR fault. It sux, but it's true.
Many years back, I was pulling a gear trailer behind a crane. The hitch broke and the trailer went off on its own. Hit a utility pole and parked car, and some of the gear fell off the trailer and into traffic. The lady closest behind me was able to stop in time to avoid the debris/gear in the roadway, but she was rear-ended and there was a minor chain-reaction involving 4 cars.
When the CHP showed up to help with things, he determined (rightly so) that my company was responsible for the parked car and the utility pole, but everything else was the responsibility of the other drivers for following too close. 2 of them sued the company, but the judge agreed and dismissed the cases.
If the box-springs had hit the car, then that's clearly the fault of the hauling driver, but if it fell in the roadway and she drove over it...that issue will get muddied a bit, and his insurance company may argue for shared negligence/responsibility...Hopefuly, they'll just step up and cover all her costs, but don't count on it happening without a fight.