Thanks for all the guesses. I hatched the white one myself, but the other two I bought from Coastal Farm and Garden in Oregon City. They have hundreds of chicks in the spring and there are always kids picking them up and walking around with them. I'm sure many get dumped in the wrong bins as so many breeds look similar when they are chicks. I'm sure many chicks are mixed up there. I didn't really care, but since I got her out of the SS bin, I had kind of hoped she would be one!
Well, I'll have to stalk the ladies and see who's laying what. My sister had a EE lay brown eggs so I know that is possible and the white one may lay blue or green eggs. I thought until posting this thread that the brown one was a leghorn. It makes sense now that she's not doing the squat and may or may not be the brown egg culprit. I was expecting a white egg out of her! So confusing, yet exciting.
I'll keep a closer eye on who is in the nesting box tomorrow and see if I can pin down the brown egg bandit!
**Update** Just went out and did a quick earlobe check. The brown one has white feathers in a circle in the ear area, but the lobe hanging down is red. The white one has iridescent ears, and so does the buff/white one.