All a matter of genetics, like yours. Hair color, skin color, height, hair color etc... Why does one child have blue eyes when the others have brown? This was my favorite part of 5th grade biology.
The chickens you bought her with probably arent related to her in reality.
All chickens have earlobes, some have different colors, blue, purple, green, white, pink, red. Or a mix, depending upon genetics and breed.
My cockerel has white earlobes but the rest of my birds have red or pink.