Start with having her drink some apple juice and feeding her some prune baby food. If that doesn't help her poop by tomorrow, then you can give her 1/4 of an infant suppository (cut it lengthwise, not short) rectally. My son was terribly constipated once. The juice and prunes didn't work, but 20 minutes after the bit of suppository he pooped a huge amount. He felt much better (and I did, too!).
Try prune juice. My pediatrician always said "stick to the p's" when feeding to keep things moving: prunes, pears, peaches, peas....etc... Things like applesauce, bananas and rice bind babies up a bit.