Is she mean because she is protecting them? You can seperate them at any time. Depending on the weather you may need to supply some heat if it's cool or wet.
We have 2 White Holland hens brooding some now, 10 hollands and 3 royal palms. the hollands are about a month old and the rp's a little over a week. I was kind of worried about the size difference but it was been working out fine. we put the rp's in with them as day olds, and wouldn't you know it since then it has rained just about every day. How does the weather know?????? Those 2 hens don't like me going in to feed and water, they hiss and fluff up but I just move slow and talk to them as I go.
Steve in NC