First heat for my dog?

I have a 9 month old female GSD. As far as I know, she has not had her first heat (I would figure that we would notice). When should I become worried about her? I know the majority of dogs experience their first heat between 6-9 months. Also, what signs should I be looking for, so I can take precautions with her around other dogs? She is a long haired GSD and you can't really see anything down there, so I think it would be hard to spot any swelling. At this point, I am just waiting to notice some blood. Any thoughts and help would be greatly appreciated. Thanks!