If your niece is into drawing unicorns, fairies, etc., I would second everyone else’s reply and say that Photoshop or a comparable program is the way to go. I used Paint Shop Pro for many years before I switched to Photoshop, and I’d say that it’s an excellent substitute for Photoshop. So your niece might want to stay with that program for now and try the larger canvas suggestion. It might bog the computer down a bit, but it’s verrryyyyy hard to reproduce the true “look” of a digital painting in Illustrator.
However…if what drove her away from Paint Shop Pro was the logo she created, then that’s a different problem. Logos are usually in vector form, as they must be adapted easily for use in print, on clothing, on the product, etc. I remember that when I made the switch to Photoshop back in 1999, Jasc (the maker of Paint Shop Pro) came out with a version of PSP that allowed you to create vector graphics that can be resized up or down with no loss of quality. I remember this tutorial I saw years ago that showed you how to do a cartoon cat in vector form with PSP. Lemme google for it…
Ahh…here it is - Vector Graphics in Paint Shop Pro 7. The tutorial also has a good explanation of the differences between vector and raster images. I’m not sure if the current version of PSP still has the vector graphics capabity and if they do, I don’t know how sophisticated they are. But it’s worth it for your niece to go back to PSP, look at the cat tutorial, and think about the possibility of redoing the logo with that method.
In the end, it will help her to know how to do both raster and vector images. I go to an art college, and everyone in the design department - graphic designers, architects, etc., knows Photoshop and Illustrator. Not one or the other, but both. Photoshop is often used for treaking the properties of photos, photoshopping our 3d models of buildings into pictures of building sites (for us architects)…lots of different applications. Illustrator is used for making logos, laying out our presentation boards, touching up line weights in a floor plan…lots of applications for Illustrator as well. In designing and presenting a building, I’ll often have to go back and forth between those two programs.
It seems like a lots of computer savvy kids and teens these days have a firm grasp of Photoshop, but very few know Illustrator well. If your niece becomes familiar with doing vector based graphics, not only will she gain a new useful skill, she’ll also be well ahead of her peers in terms of computer graphics.