Lots of bitches come off food right before they're ready.

Take her temperature to see what it is (usually drops right before delivery). If you're nervous, a vet exam won't hurt, but unless something is seriously wrong the best thing you can do is keep her calm and quiet. If she gets anxiety in the crate, then open the door and let her run loose so she's happy. When the time comes, she will go in the crate on her own.

Jack