So YellowMickeyPonchos, you were right in MY neck of the woods today! You could throw a rock and hit me from there, that is how close I am.
Anyway, I think we were not sure if the OP was going to be renting a car to go to the American Girls store/cafe, so a PP suggested the train. I would suggest that if you DO rent a car and drive to The Grove from Anaheim, the easiest and fastest way, in the fewest steps, is to take the 5 north freeway to the 10 east freeway, and get off on Fairfax heading north. Just take Fairfax all the way up to Third Street and there you are.