And rigid square/rectangular things are easy to move without picking them up. Put it on edge, grab a corner, push it forward. Grab a corner, push it forward. Or, pull it towards you, rather than pushing. If what's inside isn't loose (which if it was packed with blankets and pillows, it would have been solid) and isn't breakable (Gannon, sadly, was not considered precious by her), it's a good way to move heavy boxes.
EDIT: Either that, or 'walk' it like a refrigerator. Left, right, left, right.
Up and over a barrier is another thing, but that's one big push, squat, use your whole body like a spring, or even get your shoulders under it. But I think she more likely got one corner on the barrier and pushed the corner opposite it, in front of her, away from her until it went up and over.
