Generally, a school or an employer (e.g. if the attacker were a teacher or other school employee) is not responsible for the criminal actions of other people. The school would only potentially be liable if the school were negligent, or unreasonably careless, in some way. Examples would be if the attacker were a teacher, if there reasons to be suspicious of him (e.g. allegations of improper behavior), but the school did nothing; if the attacker were another student, if the attack were successful because the school did not adequately monitor students and no one noticed your daughter was not where she was supposed to be for an extended or unreasonable amount of time; or if the attack occured because some room or space was both unmonitored and unlocked (like a gym or band room, that should be locked when not in use) and that's where the assault occured; etc.