Manga artists: I have a 13yr old niece that I know loves manga art, is learning and has room to grow, looking for a Christmas present: should I get

It depends on what you are willing to spend. Professional quality markers made for anime are best, but they are pricey. Don't get alcohol based markers. Prismacolor has brushtip markers that are really good, but they are about $4 each. My recommendation would be Prismacolor colored pencils. They are still expensive, but much cheaper than the markers. They are also better for newer artists. Besides, you can get 40% off coupons at Michael's. It makes them more reasonable.