and she wouldn't mind a teeny gap between the hooks (like 1/8" or less) and the marble surface, she might want to try something like this:
http://www.command.com/wps/portal/3M/en_US/NACommand/Command/Products/Product-Catalog/?PC_7_RJH9U523080QE0IIHEICN90GC1_nid=3LM48754NTgsF0GFSQ26BSgl1FPR97QXHPblThe link is to something called Command Picture Hanging Strips. You can get them at Lowe's and Home Depot, and they are cheap (under $5). You can cut them to size as well. The stick on securely, and the adhesive leaves no residue. You can peel them off and reposition them with no problem. They work sort of like velcro, but are much stronger.
I had a similar problem where I wanted to hang a medallion on the granite and tile wall behind the sink in my kitchen. I also didn't want to drill holes, and in my case, wanted to be able to take it down easily to clean it and clean behind it, so I had to think "outside the box." This solution worked perfectly. The medallion stays put, and I've had no problems whatsoever with using this product on my granite and tile surface.
If it didn't work for her, there would be no damage to the marble, and she'd be out less than 5 bucks to try it out.