K.R.
If she's anything like my son, you might also want to pay attention to the kind of milk she drinks. His BM were always hard as well, unless I'd given him prune juice regardless of how much water he'd had that day, or how much fiber and avoidance of foods that cause constipation. A simple switch to soy milk fixed it. There's something in the cows milk itself he can't properly digest (he's good with cheese but not ice cream etc).
If the water doesn't work, you may want to give that a shot. Although, I think the water will help by leaps and bounds.