Can kittens heal themselves from milk diarrhoea?

It is possible. However, it also depends on the cat’s constitution. If a kitten has diarrhoea from drinking milk, fast it for half a day, then feed it some clean drinking water and also give it some probiotics to regulate its gut. After that, feed her some easy-to-digest, tasty liquid food. Monitor closely and take her to the vet if the diarrhoea does not improve.