If drawthru is your only requirement, then any one of Wacom's line will do. My old Intuos does have a somewhat useful feature for drawing through though. There's a transparent sheet on top of the tablet and you can slip your drawing under it to drawthrough. However, you can do this just as easily with the cheaper tablets - you just need to tape the drawing to the tablet; the pen can easily work through it. Some actually prefer taping a paper on top of their tablet permanently, as it gives them the familiar paper texture they're used to, when drawing with pencils.
I actually think that the differences between models have mostly disappeared in recent years. The absolute cheapest tablets may have less pressure levels (however, I've heard many talented artists say that it's not a huge loss), less function buttons on the tablet and you can't purchase additional tools (for example the airbrush tool), but that's about it.
A graphire or the new bamboo would suit her best, I think.
.. actually, I just browsed to the European homepages of Wacom and I see that they don't list the Graphire anymore - maybe they discontinued the line and replaced with the Bamboo. In any case, you can't really go wrong with any Wacom tablet - just pick the one you think is the best size and price for you (or her, in this case).