For her age, and not breaking bank, a thin tipped capacitive stylus pen will do if you are in the budget realm.
Of course, to be better at art, half the battle is understanding composition, style, perspective, and the mediums at hand as well as all theories. The other half is practice. The tools will ultimately determine how much distance one can take their skill level - much like a performing racing car versus a standard commuter.
Still, the only other bridge I can think of from touch finger art with an iPad is quite possibly the Venue 8 Pro (not bank breaking like the Wacom enabled Surface Pro) but has the optional pen that eliminates disconnects that exists from standard drawing digitizers that connect to a computer. Wacom also makes styluses for the iPad too, albeit battery powered - thus being heavier than their non-battery powered solutions.
Hardware is only HALF of the solution though. Painter Lite can mimic and emulate traditional mediums at a very cheap cost. Art Rage also does this too (though the brush options aren't as extensive as Painter). While GIMP is a good free image manipulator, it does not compare to Painter and Art Rage. Both are more apt to making things from scratch and "draw" better than GIMP.
If she is drawing and painting alot, these tools can give her all the practice she needs, without spending quite a bit of money (and cleanup) on traditional mediums - while allowing her art to be stored without taking physical space and is preserved much longer. That is the BIGGEST benefit of digital creation. Then if she wants to test herself, break out the canvas and let the 'translated' skills of Painter Lite and/or Art Rage come to test (those programs near replicate the mixing feeling and painting feeling and have a better chance of translating to physical mediums than GIMP does).
And of course, there are plenty of online videos for instruction. Even better if said video is side by side on the screen while she paints and draws. Hence ultimately, despite being a VERY EXPENSIVE upfront cost solution, a Surface Pro would be something that will last for years to come and allow for more extensive upward growth. But I don't think this is within your budget at the time being - but it is well equivalent to the amount for any paints, canvases, and physical mediums.
Since you have a computer already, let her try an inexpensive Wacom USB digitizer. But also look into Painter Lite and Art Rage, she will appreciate the near replication of art tools on those programs versus GIMP.