Dried blood around female boxer's cage?

I have 3 dogs - a male and 2 females. Both females have been spayed for several years. The female Boxer sleeps in a kennel between her mate (male Boxer) and a female terrier. That's where I found this tarry, blackish purple colored stuff in a thin layer just outside her cage this morning. It was dry and flaky looking. Just yesterday I'd washed out all the cages. There was also a small pile (this morning) of what looked like might be excrement, also tarry and blackish. So I'm suspecting a bloody stool. I washed it out after work and it had that bloody smell similar to when she gave birth to her litters. She's 8 years old. She wasn't her peppiest today but then again, didn't seem to be sick either. What could be going on with her?