If you want something slightly more complex but still light, I think a game like Splendor is would be a good option (it's about the same level of "difficulty" as Skull King).

Dominion (and its many variants/expansions) is really fun, but may be a bit too complex for your grandma. Same with Seven Wonders Duel (which also has the drawback of only being a 2-player game).

I second the comment above about Sushi Go or Cover your Assets as well. Both should be pretty simple games that your grandma should be able to pick up.