My son had this problem when he started solids. The GP recommended suppositories to ease out the poo. And lots of fibre and water to make the poo softer and easier to pass out.
You can try adding some psyllium husks to her food, just sprinkle a little bit. Psyllium is full of fibre but like all fibrous foods you need lots of water. Oranges are great for getting poo out too.