Two of the facts released by police are that cuts to two fingers were self-inflicted, and that there is blood on the passenger seat and inside passenger door panel of the car.
The only way that makes sense to me is if there is evidence of how Cheryl caused those injuries to herself, such as blood on a panel or sharp edge in her car. What I mean is that if police have the object that was used to inflict the injury, and combine it with the injury, there must be some circumstance that allows them to conclude that the injuries are self-inflicted.
Alternatively, if someone is strangled, perhaps they have self-inflicted injuries to two fingers while fighting a rope, or wire. Perhaps that would be a defensive wound.