Well I'm a little new to the concept of EE...
But it seems that because she's only half Ameraucana her eggs might not be EE, right?
Unless it's for certain that the egg colors of the parents would mix and some sort of greenish blue color would emerge...
But she has those little puffy cheeks so we know mom was Ameraucana. I can't be certain but I think the man who sold them would know Ameraucana from normal EE because he also raised show quality serama's so he seemed to know his stuff.
With those cheeks?!?!?!
& a Pea comb to boot!
Thats an EE!!!!!
If mom was an Ameraucana, a decent one will be carrying 2 copies of the blue egg gene. Which means she had to give it to your little one.
The Buff orp will be carrying brown egg genes.
As Orp eggs vary greatly in the shade of brown, the only question is what shade of green your baby will lay!
Since your new to the term EE...lemme give you my version which I have come up with through extensive research

EE's, or Easter Eggers, have no breed definition and are not recognized by the APA. Anyone who calls them an unrecognized breed however I would call wrong! The best poultrymen in the business will look at an off colored Ameraucana and tell you "That's not an Ameraucana, that's an EE". Seems to me they are recognizable?
EE's have been around longer than either Araucanas or Ameraucanas - & were talking for decades before either was "recognized" as a breed.
Some people have personal standards for them, personally I Like them with beards and combs, and the blue egg gene - but they are not called blue/green egg layers, are they now?
Is a Buff Orp/Wyandotte cross and EE? NO - that'd be a "sport" or a mix! But it seems some just want a breed name for their mixed up chickens, so they call them EE's.
& that's OK with me, some of my prettiest hens and best layers are mixed up chickens - I have a Black Copper Marans/Aeraucana/Silkie Roo that is my best cock bird!
None of his offspring lay blue/green eggs, so I'd say he has lost the gene?
The best thing about EE's - no-one can tell you they aren't EE's !!
BTW - I had 3 new EE's this week

Black one a white chipmunk and a golden chipmunk from a green egg!
Welcome to the EE Club!!!!