This is the backside of her next to her other "Americauna" sister Henrietta. I don't have other good pics of Henrietta but have no clue what breed she is either.
X2 on Gertie being a Buff Orpington pullet. I can't see her comb very well, but Henrietta, who is standing next to her in the top pic, appears to be a Black Australorp. Both of those are excellent breeds; very hardy, calm and gentle, and good layers (Australorps in particularly excellent layers).
The black bird's most likely an Australorp. You won't get the pretty colored eggs, but I think other than that you'll be very happy with each of those breeds as backyard birds.