This was rather local to me and there was a lot on FB about it. . .the horse was healthy but 27 years old. Apparently the 'yotes spooked her, she slipped and fell on the ice, and once she was down they attacked her.
A lot of coyote hunters have been jumping in and offering their services. One posted a pic of a coyote they had killed in Shiawassee county (nearby). It weighed 75 pounds. A pack of those could take down something pretty big.