it could be the food is a little too hard for her gut just yet. I would be tempted to stop the solids for a few days and try giving her some cool boiled water in addition to her formula and see if that helps. I'm assuming you know all the massage techniques that can help her so I won't repeat them all here, except to say the one I found most helpful when my son was constipated was massaging around the outside of his anus in a circular motion (feel free to wear gloves, it can start a poo-splosion).