Flower essences are not oils, they are extremely dilute solutions made from specific plants (kind of like homeopathy - works on an energy level). They're fabulous for cats and can be administered in food, water, spritzed on bedding, dabbed on ears or forehead..... no side effects and completely safe. NOT to be confused with essential oils, which are a very different thing and can indeed be toxic to cats.
http://www.bachflowerscanada.com/pets.htm
http://store.jacksongalaxy.com/