I would assume she is in heat. Maybe she is just a light bleeder and she is cleaning herself well...
My Gracie just had her first heat and it went by really lightly but the physical changes in her and great. Coco would not even go near her...I was so worried about him going crazy over her scent like he did with Trini and Shayley. But he smelled her and then walked off snobby, like, "No, you're too young, for a man like me" LOL...and tried to hump Trini, lol
She didn't mind...