We've all heard the rare story of a four-week-old baby who sleeps six or eight hours at night, but this is not typical. Most babies do not get to a point where they can sleep six or seven hours at night until they are at least three months old. Very large babies sometimes can do this sooner. When a baby hits about 13 pounds they often show readiness to sleep through the night.
What you do want to start working towards, however, is getting the baby to go right back to sleep after waking at night to eat. A lot of babies have their days and nights reversed when they first come home. They are awake and alert at night, and sleep a lot during the day. What you want to try to do is train the baby to be up more during the day, and to sleep most of the night, only waking up to feed and then going right back to sleep.
You can work on this by keeping things quiet, the lights dim, and trying not to let her get too agitated at night. In contrast, during the daytime, you should keep the shades up, allow all the usual household noises, and do a lot of talking and playing with the baby.
Over a few weeks, most babies adapt to this well, and spend more and more of their nighttime hours sleeping.