If you have leather furniture that she has marked on, a good place to go for help is http://www.thatleatherguy.com and contact a guy named Todd, who has been in business for thirty years. (By the way, this is not Todd writing an ad for himself - it is his bride speaking. I'll grant you that my opinion may well be prejudiced, but I can tell you that he is well-respected and well-known in the trade, that really knows what he's doing, that he won't take your money if it's not worth it for you to fix it.) Speaking from my own experience with leather furnishings, it would not be recommended for you yourself to attempt to clean something off leather without your first knowing what kind of leather you have (there are over 200 kinds of finishes, so it would be difficult for you to know) and what it's tolerances are (some are cleanable, some are not). And the technique used to remove marker, etc., would depend upon what your daughter used to write with.
I empathize with your daughter's urges - I distinctly remember being caught drawing with red crayon on my mother's soft green wallpaper. I thought I was beautifying the wall, but I quickly found out Mother did not feel the same way! :)
As for a solution about restricitng access to the markers: how about keeping them in a little cash box or tool box that has a lock on it. That way even if she finds their hiding place, she still can't get at them. Can't imagine that what's in those permanent markers is really very good for the body, so I'd be in favor of taking a strong measure like that.