Very good. Since she likes art/paintings, I could suggest Behind The Frame: The Finest Scenery. It has a great narrative and doesn't take too long (2h). Not sure if I would put it in the top3 but thats your decision anyway. Good luck. South of The Circle is another narrative game which left me pondering. I think thats the perfect genre for her anyway, whether she uses the word art or not ;)
I don't know if you enjoy such games, but I also found here on HN some 2 player games like It takes two. Perhaps she would enjoy it? The story itself is not my cup of tea but I still think the game is great.
I was debating whether to specify which one, but then decided I would leave ambiguous.
Frankly, they're both great. I think I have more of an affinity to Portal 1, not because it's "better", but because it was first. That was a very distinct moment in my memory when the game mechanics "click" at the beginning, and you realize what's going on and there's no other game world like it.
