Joan, if she has a large budget to spend on this, the best tablet on the market is the
Wacom Cintiq. The 12" version is the one I use to draw everything these days. The beauty of these is that the drawing surface is also a screen, and to all intents and purposes you are drawing directly onto it. I've used tablets for a quite a few years now, and it's the only one I've found that I can draw from scratch with - I've never quite mastered the hand/eye coordination that drawing with a conventional tablet requires, although I can use them for inking in scanned pencil sketches, and colour work is a doddle. they do, however, cost a small fortune.
The best of the conventional tablets, in terms of value for money and ease of use, in my opinion, is the
Wacom Bamboo. There are a number of versions and sizes in the Bamboo range. I've owned two (Bamboo Fun and Bamboo Pen & Touch), and both score very well over their more expensive peers in the Wacom Intuos range - I have an Intuos3 A5W, but never rated it that highly because of its 'slippery' drawing surface. Not only is the Bamboo half the price of the Intuos, but the drawing surface has a 'drag' that makes the penmanship feel more natural, and I actually found the line to be smoother, despite the pen having half the levels of pressure sensitivity of the Intuos tablet.
I hope that's of some use.