
Are you sure she did not accidentaly get caught out bu a male dog ??
If not she could be having a phantom pregnancy. If that is so you should watch her and if the teats become very hot and swollen. She may also be starting to produce milk. I would take her to the vet and he will perhaps give you some medication for her as she may need help in getting rid of any milk that she may have .
These false pregnancys can lead to other things if not taken care of like womb infections ( dont mean to get you worried ) so just keep an eye on your girl.