I'm a little concerned about the fact that you are describing it as black. This sounds like something called melena, which is a free bleed or ulceration in the intestinal tract. The body digests the blood, and it comes up black.
I think that you really do need to see a vet on this one, just to rule out this problem. It is important to take some of the feces and vomit in to have them examine it. They'll likely need to do what is called a PCV at the very least. This checks for anemia, and is important if there is bleeding. Depending on what they find, there are some simple medications and treatments to get this under control.
Alternatively, it is possible that she got into something that is black, and that is causing the discolored vomitus and feces. But, I'd probably not take a chance. If it is a free bleed, this can progress and become potentially fatal.
Please see your vet, and let me know what they find.