A bitches first season can be a bit 'funny' in that it doesn't always follow the rules ;-) She may just be pre season. This can be a week or so before she actually comes into season properly, or she may be keeping herself very clean, which is why you aren't seeing any blood. Some bitches don't bleed too much with a first season, others will bleed like there's no tomorrow
I would still keep your male away from her. If they do mate when you aren't there to supervise you could end up with seriously damaged dogs. :-( If she pulls away from him when tied he could rip himself badly, and that will not be easy to heal. She could also do some damage to herself, which again is not easy to heal.
Why do bitches always come into season at the wrong time? I have one in season just now and will be at the height of her season when I get my new kitchen put in ;-) Oh, I also have an entire male in the house :-D