A 9 week old kit should have only just left its Mom, so constipation is a very serious concern. It may be dehydrated, or ill. This is a baby that has only just started to eat solid food. You need to consult a vet, this is not normal.
Get a can of any brand kitten food. take the can of kitten food about half of can but some the kitten food on a plate. give about half a teaspoon of the mineral oil and mix in with can of kitten food
This baby should be barely off milk feeding, I question why you have decided it's constipated. Feed her some pure, non flavored yogurt daily, provide water at all times, and let nature take it's course.
If your kitten is eating normally, you can try massaging the kitten's abdomen. Also try to add some vegetable baby food (ex. squash) to their wet food for extra fiber.
The most likely problem is the kitten isn't drinking enough water. Make sure water is always available. Kittens also need soft food, so feed canned or moistened food.
