Kittens should defecate once or twice a day but I would not become seriously worried unless she went 48 hours without, especially when she is so new to your home. The sudden separation from her mother and playmates will have left her slightly stressed even if she is settling in well. This can have a knock on effect on her entire system including how often she defecates. A sudden change in diet can also have an impact on bowel movement.
There is also the possible that she has in fact been defecating but you are yet to discover them!