YOU HAVE NO IDEA HOW LONG I'VE WANTED TO ESTABLISH THAT SIDE EFFECT AS CANON
*Erhem* But yes, Rhoda can't just run around solving world hunger by making food grow. Anyone who eats them will grow bigger, and they won't ultimately get more nutrition out of it. Granted, she could make the food smaller, but that would presumably a) make people shrink, and b) not solve anything beyond making oversized sandwiches and burgers more manageable.
Oh, and I guess she knows she has magic now, and Catalina knows about it, too. I GUESS that's an important detail.