My little girl, 12 months, also has had problems with constipation. I made sure to mix her cereal with enough water and sometimes used prune juice instead of the water. You might try giving her additional water in a sippy cup to make sure she's getting plenty. You might also want to try juices. Pureed prunes, pears and oatmeal help things move. Bananas slow it down as does rice cereal. With the pureed prunes, start with a little and work up to larger amounts gradually.
It sometimes feels like you're Alice in Wonderland, feeding your baby a little of this and a little of that to find the right balance. Try a couple things to see what works for your daughter. Good luck!