To be honest, I don't want anything for this. If you can, take her to an emergency vet. If she does have problems digesting, she may be constipated. If so, the toxins could be harming her. If impacted, she needs to be seen ASAP. If she was very small, her digestive system could be underdeveloped. As a result, she's not able to digest the food properly. Softer food would be best. As for the falling down, it could be related or ther could be something else. In any case, please write back and let me know.
Good luck