You might not find her clothing in baby sizes (not sure) but it's cute! You'll certainly find something for the infant in the Corte Inglés. Last year I sent a friend the cutest shirt with counted-cross (sorry, can't describe it). Anyway, have fun!
There was an Agatha Ruiz de la Prada shop in Barrio Salamanca a couple of years ago. I wonder if it's still there?