The decision whether to report to the police or to file a Title IX complaint always lies with the alleged victim. You can do one, both or neither. One does not preclude the other. Whether one is preferable over the other depends on the individual and the circumstances. I would advise both.
An off campus act is covered as far as I know but the alleged perpetrator has to be enrolled for the school to have jurisdiction over him/her. If the perpetrator is not enrolled at the school they may still have some notification responsibilities – see page 9 of the document I linked above.