The best way to move someone who's incapable of walking is a wheelchair, but we don't have one.
But using items in the cellar, you can make something similar. It may look like a wheelbarrow, but it'll do the job.
You'll need five items from around the cellar: something for Harper to sit in, something to steer with, two wheels, and something to hold the wheels on.
After you stop talking to Jess, you're looking at a defunct mine car. That takes care of item one.
Back up and turn right, and you'll see wheel one on a shelf under and to the right of the light on the wall.
Turn right again until you're looking at another mine car. See that odd shape on the floor to the right of it? They're old bicycle handlebars, and they'll work fine to steer this device.
Keep turning right till you're looking at Jess and Harper. Wheel 2 is on the chair to the right --
-- and you can find the bolts you need on the shelf behind them.
Now turn back to the mine car and assemble. The right order is --
Both wheels, then bike handles, and then bolts.