I think it depends on your child. Is she truly "gifted" or just "smart" Our school mixes up the kids, too for homeroom and language arts. They are segregated for math, social studies, and science.
Pros: they are not stuck with the same kids all day for 4 years as in other LL4.
Cons: language arts or other non-AAP classes will not be as challenging. Our school still differentiates for language arts as they did in 1st and 2nd grade (different reading groups, for example). But, that's different than a whole advanced class discussing a piece of literature.
For us, it is not a problem, because language arts is my daughter's weakest subject, so she is fine being mixed in with non-advanced kids. She's also very social, so she enjoys being in class with her non-AAP friends.
But if my kid were very advanced in reading/English and off the charts on all subjects, I'd probably not put her in LL4 even if they didn't mix them up with non-AAP kids.