From my experience, when they are that young, forcing them to stay awake can actually make their sleeping habits worse than if they are allowed to sleep when they need it. As someone already said, newborns need a lot of sleep, and should be allowed to sleep when they need to. That's the way babies develop a routine. I know it worked for us. My daughter is a year and a half old now, and we let her sleep when she needed it when she was a newborn, and since then she has developed a good napping and sleeping routine. And I'm due in July with our second and I know we plan on doing the same thing. But sometimes having a newborn is a lot tougher than you expect, and if your sister thinks it's a good idea, then maybe just suggest to her that she ask the pediatrician what would be best. Maybe they can suggest a better routine for her and the baby. Good luck!