Vet. Don't bother looking about online, get your dog to a vet.
HGE can kill. It can kill within hours. If your dog is having that much diarrhea (and darker blood means its from higher in the system) and is vomiting that much (water does no good going in when it comes right back up, it means it isn't getting absorbed, and you have further losses with each vomiting episode), it just means get the dog into someone sooner rather than later.
It could be at this point anything. Forget the why. Worry about the what and get her medical treatment. :/ You can talk about the why later once she's more stable and her insides aren't acting shocky.