I suspect that this claim fails. Your daughter may certainly pursue VS through CEDR and then MCOL if CEDR fails, but the essential issue here, e.g. a carrier's responsibility and ability to regulate the perfectly legal activities of its employees while off-duty is a hard series of inferences.
You have not specified the activity, but it seems overbearing to suggest that carriers ought to parse activities, e.g. what if the FO had broken his leg on a run, what if it was while parasailing, and what if something inbetween. This can be juxtatosped against acitivities where there are clear bright lines linked to specific abilities, e.g. alcohol and illegal drugs.
The essential issue here is that on a rare and unpredictable basis, things happen. This is at an outstation and there is no reasonable way to find reserve crew, so it really is "extraordinary".
So, the real question for your daughter is whether she has the time to pursue this against the likelihood that she will prevail.