Did you get the other drivers plate number? If so, have your sister file a claim with her insurance company. Have them run an insurance check on the other party. See what they come back with and file a claim with the other parties insurance company.
They will complete the investigation and even if the other girl says it wasnt her fault, her insurance may determine that she is at fault and pay the claim. If not, your sister will either have to file her own collision claim on her policy or get it fixed herself.
Were there any witnesses? Also how where the police called? Get the phone records that prove she called the police. At least it will show she made the attempt.
These steps wont guarantee that the other girl’s insurance will cover it, but it will make their chances better.
ya now that i think about it shes fucked either way… paying the deductable or paying out of pocket… insurance sucks… glad my soob is unmolested and in a safe place