
I would say she is already or about to come in season. I would check her every morning by blotting her vulva with white tissue, as you may miss the blood discharge, as some bitches bleed little, and can be very good at cleaning.
From th4e first spot of blood on the tissue keep her away from male dogs for at least 3 weeks, until outward signs of swelling subside.
If your dog is entire then he will need to be kept away from her at all times, and to be safe for four weeks.