Simple painting app for a grandparent?

Brushes and the like are too complex. But my grandmother’s an artist, so the “kid” painting apps I’ve seen are too basic!

Any recommendations for something in the middle?

The ideal:

* No more than 3 or 4 buttons/options on the screen (my grandmother is not a computer user at all)

* Full-screen painting mode

* Full color wheel (not RGB sliders) or at least a very large palette of pre-defined colors

* Multiple brush sizes or styles

* Undo/redo

In other words, the simplest possible UI... but not skimping totally on the features.

Photo importing, layers, etc. would be overkill.

Thanks in advance!