Hi, Vicki,
No this is not a sign of her coming into season.
If you are sure that she is not actually pregnant this is a sign of a 'false pregnancy'. She would have been in season some 6 - 8 weeks ago, and her body is kidding her that she is going to have pups. She will probably make a nest, and cuddle some small toy or object as she would a puppy.
It will probably settle down in a few days, but your vet will be able to give you some treatment for her which will disperse the milk.
If her milk glands do become very enlarged and uncomfortable, and you do not intend breeding with her, you may consider having her neutered to prevent a recurrence in the future.
Walter