Here's a link with info on why and how to clean a baking stone. She can probably soak it clean.

Here is a link that might be useful: Cleaning a baking stone

I don't know if this will work for soap, but ours smoked like crazy after getting olive oil on it. We we're ready to buy a new one, but instead put it on our gas grill outside, closed the cover, and "cooked" it for about 20 minutes on high heat. It no longer smokes and works great.

PS We never wash it, and only clean it by lightly scrapping any residue off after each use.

First bake it on a grill like svwillow suggests at least until the stone stops smoking. Follow that with a soaking in water as momj47 suggests. Baking it will burn off the hydrocarbons from the soap's molecules and any other oily residue within the stone's pores. Baking will leave behind a caustic ash residue that the water soaking will then be able to remove. After the water soaking, bake in an oven at 250 degrees F until it's dry. After this treatment your stone will be as good as new.

Soaps/detergents do not remove seasoning......it can only remove oily residues. Soaps/detergents are absorbed into the baking stone's pores when they are used for washing. The absorbed soap/detergent will later thermally decompose in the hot oven when the stone is later used. The burning of this soap/detergent residue can give food a nasty flavor. Moisture within the raw dough can also pick up the soap/detergent residue into its crust. So......as others have suggested, don't use soap or detergent on a baking stone. It isn't necessary to ever clean a baking stone if you keep it in the oven at all times.

Dan