In my state refusal of a breathalyzer after a DUI arrest results in the loss of driving privileges for a year. Period. While one can ask for a hearing, the penalty almost always stands. Refusal is considered a breach of law. And yes, a warrant could be obtained for a blood draw.
But in Anne's case, could specific times of use of drugs be determined by the coroner? Pot, for example? It was reported that was in her system but does that mean she ingested it before driving that day? For example, this link suggests "testing for marijuana especially in urine, detects evidence of use, not current intoxication.." Do other tests show current intoxication? The fentanyl reportedly detected was thought to have been hospital-administered but I thought that was based on the likely need for painkillers and hospital records, not a test that said when it entered her body.
JMO