The dog has bitten a friend of my daughter.
Rover Support, as Deb wrote, and the owner should have been contacted. On my intake form, I ask whether the dog has ever bit anyone. It would be very useful knowing if this had occurred before and if the dog shouldn't be around children. I don't know what the owner put in the dog's profile, but if the dog has issues with children--or cannot be trusted around them--then they're being highly irresponsible/negligent and should be looking for sitters without children.
Once again, another reason why sitters should have access to previous reviews. If this occurred on another Rover-arranged job, then Rover would share in the negligence, as they took no steps to prevent another incident.
Oh dear. Have you tried calling Rover Support yet? I think they can advise you best, especially since they might have useful information that you might not have about the dog with any past bookings. Until you get a hold of them, I'd suggest restrict this dog's space (ideally with dog gates inside) for the safety of all.