With regular chick starter and nothing else, you really don't need grit, but a sprinkle on their floor is fine. They'll pick it up. Some starters may have grit in them-it would be on the ingredient label, though, or should be. I've never given them grit here, personally, though it's fine if you don't do more than a pinch. Mine are usually out on the ground with mom and they naturally pick it up.
As far as the heat, could be it's too warm, yeah. Maybe she is just different though, maybe larger or just more hot natured as the others. If they all have room to get away from the heat as they grow, they'll regulate themselves.
The reddish ones look like Speckled Sussex. They have a single comb. Hard to ID EE chicks this young, really. So many look like other breeds.