There's at least one story element she won't get if she plays the sequel first. I'm not sure how vital this part is to the story as I haven't finished the game myself yet, but she'll definitely have parts from the first one spoiled if she plays the sequel first. AFAIK, it's not a disaster if she plays the sequel first though. Outside Layton and the kid, 95% of the story seems independent from the first game so far. Is the reason why you want to get her the sequel that you've played the first one and want to play the second one with her? If not, I don't see a reason not to get her the first one first!
Scribblenauts is definitely awesome. Harvest Moon DS and Island of Happiness was quite dull compared to other Harvest Moon titles. Wario Ware: Smooth Moves is fun, but might not be her cup of tea if she can't handle fast paced games. A Phoenix Wright game perhaps?