This is a very important question during this pandemic. The answer is that it is your sister’s choice. Absent a court order to the contrary, your sister can live and receive care wherever she chooses. If she is not competent to make that decision, it is up to her agent under a health care proxy or durable power of attorney for health care. If she hasn’t appointed an agent, some states designate decisionmakers based on their relationship to the patient, but other states do not do this.
Absent an appointed or designated decisionmaker, if the family is in complete agreement, the hospital may defer to them. Or they may require you to go to court to be appointed guardian to have the legal right to make this decision on your sister’s behalf.