I would try a weak solution of bleach and water - say 1/8 of a cup of bleach to a gallon of water. I Usually say 1/4 cup, but the bleach may bleach out the print/colour on the paper.
She could try 1/4 cup of bleach to a gallon of water, however I would use it on a spot of wall which is not seen (like behind the toilet) first and see what happens.
Though vinegar will remove the black, it will not kill the mold spores, thus the mold will grow again and again.
It is very possible that the mold/mildew is through out the paper - Wallpaper is porous and in the moisture of a bathroom becomes a breeding ground for many wondrous life forms - I always suggest faux painting or solid colours of semi-gloss paint in bathrooms with the addition of say a temporary wall paper boarder.
Cheers
David
Posts: 4018 | Location: Leaving land, heading for the ocean | Registered: 06-03-02
vinegar does kill mold, and it will less likely harm your wallpaper. But I would not dilute the vinegar. It will not leave a lingering smell. Bleach will.
Posts: 1866 | Location: MS gulf coast by debris pile | Registered: 06-05-02
Once you remove the mold, make sure you keep your bathroom well ventilated. Crack a window or turn on the exhaust fan when you take a shower. This will help keep the moisture levels down and will help prevent the mold from coming back.
Posts: 5308 | Location: The Motor City | Registered: 06-03-02