D.D.
If it's acute (she's really crying and can't get anything to move) you could do an infant glycerin suppository (PediaLax has them). It will work within minutes. Then, once she passes the hard piece that has her blocked up, keep up the prune juice, etc, to keep things moving.
Also in the longer term, watch what you are feeding her. If she's started solids, stay away from rice cereal. You can see if oatmeal cereal is easier for her system.