I would suggest you get her some peel-off (usually soak in warm water and peel off) or water-based nail polish (can be removed easily with adult supervision with isopropyl alcohol or pure alcohol) and brushes and real nail polish stamping tools (engraved metal image plate, scraper, stamper). This will develop her hand-eye coordination and keep her more active than would a few-click computer game. Another option for her would be acrylic paint, which is often used by adults, hobbyists and professionals alike, who do nail art. Acrylic paints are water based and can easily be washed off with water. If you permit her to wear polish for a more extended period than play-time, her acrylic nail art creations can be preserved by topping them with a peel-off, water-based, or conventional clear top coat. The plus is that any mess on other parts of the fingers is easily washed off with water once the clear top coat is dry. With acrylics it is also easy and comparably inexpensive for her to practise ideas on paper before taking them to her nails. Like with other such projects, supervision and a papered area where all needed components are at hand before getting started are crucial. And for most polishes, she'll have to understand that waiting for it to dry will be part of the process if the wants her creation to stay in good shape. Good luck!