Babies that are nursing or bottle feeding when ever they want tend to "snack." They aren't getting a full feeding. They also get accustom to using feeding as a pacifier, they aren't really hungry it is just soothing to to suckle.
I would work on getting full feedings from your baby and slowly start spacing out the feedings to every 2 1/2 to 3 hours which will help baby learn when it is meal time. The gap in between meals will ensure she is filling her tummy and not snacking her way through the day.
Babies who have a feeding schedule seem to naturally fall in to a sleeping routine and sleep longer periods of time since they have full tummies and they know when to expect their next meal.
Hope this helps!
Note: Pacifiers are a great way to sooth your baby when she is just wanting to suckle and isn't really hungry.