Society member has a wild pet dog that bit my sister

this dog has bitten many people and now my 13yo sister! It has become a headache even I don't feel safe around it (it has bitten my mother as well). Not just our family it has bitten few other society members and their guests. The owner always tries to gaslight us by saying it has not bitten but it's a small scratch from its nail, like we can't see if it's biting! At the time of biting my sister, the owner had its leash but it got free and charged towards my sister! It was a scratch luckily she was wearing some thick jeans otherwise it could have been more severe! What can we do? What actions can society members take? (i just shared an incident that happened with my sister and all the dog lovers are bombing dislikes on the post, the like to dislike ratio is already 54%! anyways i got few good suggestions i needed now its between that dog and me)