wilbur
>The problem with the knife sharpeners that have you pull the knife between two small ceramic wheels is that you wind up with a small hollow grind on the edge of the knife blade. This may be good for chisels or plane blades, but for a kitchen knife it can cause a point of weakness. A kitchen knife takes much more use and abuse in the kitchen than woodworking tools, so toughness is more important. A hollow grind is not desirable on a kitchen knife.

Chef's Choice makes good kitchen knife sharpeners that can be used by people with little to no experience with sharpening. They are designed to put a microbevel(!) on kitchen knives. This helps a lot with the durability of the edge.

I have one of the manual models (Model 450, about $25). Their electric ones are good, too, and start from $60 on up. They are available at most places that carry a decent collection of cookware, including Target, Bed Bath & Beyond, Macy's, Williams-Sonoma, and so on.

On the other hand, the last time I sharpened a kitchen knife (as opposed to using a honing steel), I used a Tormek to reset the cutting edge angle as an experiment, but I don't know if your sister wants to go that route. :@)