Some cats have a birth defect that results in a kinked tail. Does it bother her? If not, you might mention it to your vet the next time your kitty gets her shots. If it seems painful, however, then you'll want to get your kitty to the vet right away.
Call your vet when they open in the morning. Cats don't have very many nerve endings in their tails so they do not seem terribly bothered even by very severe tail injuries.
The problem is likely to be relatively easy to solve and your vet can tell you what the best course of action would be. It is important that she see a vet but it is not an emergency so you can wait till morning and make an appointment.