I’m not sure what size mine lays because I have a lot of brown layers but yes, I do think she lays pretty small eggs! Haha and I have several teeny tiny eggs that I don’t think are her but maybe. I think those ones might be from my old girls but idk. Have 2-3 of them so different birds.
And oh no!! That stinks!! Though Sussex are cool too and I can see how the mixup happened since they look so similar as chicks haha did you tell them?? I don’t think she is laying yet but I’m not really sure. If/when she does though I’ll get pictures!! Maybe separate her so it’s for sure her egg haha
My Leghorn is great!! She is a bit bold and stood right up to the adults at like a week old

but she’s not mean at all haha just bold, confident, and very friendly and curious. She’s so inquisitive and curious about everything haha they say they’re supposed to be flighty but mine isn’t at all and is one of my favorites. She also lays huge white eggs every single day so that’s a plus!
She occasionally gives my new birds a little bit of a hard time currently but she’s not terrible about it and I’m sure she will settle down. They’re still pretty new. She’s perfectly friendly to the other hens.
Also I think them being the new ones as opposed to the other way around will help.
One of my hens is a horrendous bully to the new birds and even one of her sisters
But she’s not a leghorn haha
The leghorn is great!!!