Normally a bird species (whether chicken, cardinal, etc etc) will lay an egg each day or two until she feels she has an appropriate size clutch to incubate. It is normally instinct for "mom" to remain away from her nest until she is ready to start the process. All eggs remain fertile but dormant until the broody begins to set. That way the early laid eggs begin developing at the same time as the last laid egg. Since your broody did not follow the norm, next time you will need to perform that task for her, by removing her "dummy" eggs and giving her a clutch. Allow her to set on eggs (real or fake) that you don't want her to hatch, until you have enough eggs that you do.
It's normal for late-hatched chicks to get left behind (and as a result sometimes die due to hypothermia or other causes). The fact she killed the younger hatchees but dotes on the three oldest signified she did see the younger hatchlings as intruders. Hopefully she will raise the original three with no issues. Still, since she Is a known chick killer for reason(s) only to her, I would be prepared to intervene by removing survivors asap and never let her hatch chicks again if she does another such misdeed. Hopefully now and in the future, she will be a great mom, as long as all chicks hatch within a day or two of each other.