Do you have to tell the police who was at a party if it gets busted?

Recently, the cops showed up at a party in my hometown in the woods. Everybody ran, and they didnt catch anyone until a girl showed up at the local gas station where the cops were waiting for people. They had suspicion that she ran (her clothes were riped from a barbed wire fence and was bleeding...and it was 4am). They made her blow and gave her an MIP. after this, she ratted out about 8 other people saying that the cops forced her to tell them who was at the party. She also ratted out who bought alcohol for the party. Can the police force you to tell them who was at a party like this? or did she most likely rat everyone out because she didnt want to be the only one to get caught. (all the people who she told on received MIPs in the mail, went to court, and their MIP's were not revoked)