You're not a judge and this isn't court... So why on earth are you asking for proof? For crying out loud... Why do people need to act so goddamn superior... Why would anyone have to prove anything to you? Who are you to ask for proof? Are you the supreme court? God? Or just an human being with the need to point fingers? Even if this didn't happen to her sister, this happens way to often to someone's sister or brother...
I hope your sister is recovering well; it's a shame how these things keep happening every day... Hope she gets the justice she deserves