Do you think that this could be because she was the runt of the litter?

she paws the bed for exactly the reason you suspect - because she was taken away from her mum at far too early an age, most kittens only start weaning at about 5/6 weeks old and even up till they are about 8 weeks sometimes like to have some milk, that's why getting a kitten 8 weeks and older is better, the pawing of the bed is because its what a kitten would do to stimulate milk from its mother's .