Gemma, Amy's doing brilliantly. Girls are usually more advance than boys in the speech department which is good to know for me cause Blake can only say:
Mum, Dad, Baa, Boo, Cat, Quack, Moo, oof (Woof), Oink, Neigh, Meiow - actually him mimics our cat more than saying the word!.

He can however sign a similar number of words, Drink, Food, Hot, Steam, Rain, Yummy, Cat, Finished, Gone, Thank you...

He's nowhere near Amy's level so I wouldn't be too worried. And by what Monnie said, it's fairly normal.