Ameraucanas are pure bred chickens with breed standards. They have tails, muffs (cheek fluff), and beards. They only lay blue and sometimes green eggs. Easter eggers are mutt birds that lay multi-colored eggs. Easter eggers can have the tail, muff, and beard of an ameraucana, and even be the same color standard. But if it lays an egg any color other than blue/green, it's an easter egger.
There's a similar breed called an araucana. They have no tail feathers, and have only tufts- not muffs or beards. They're a rare breed, and have specific standards like the ameraucana. They only lay blue eggs. Neither the ameraucana or araucana are sold by hatcheries. You can
only get them from breeders. If you got your cutie from a hatchery, there's a good chance she's an easter egger.