There really aren't many health issues that are breed specific in chickens, at least not for the dual purpose type birds, which your girl is.
there really aren't downsides IMO to a mixed breed. They're pretty and they lay well, that's honestly about what most of us want in our flock. You can't show them. You can't hatch purebred chicks. That's about it, far as I'm concerned.
Can you tell my flock is full of mixed breed birds?
X2 on donrae's post.