advice

so my little sister was recently sexually assaulted at one of my dads friends houses. obviously she was terrified and I was completely pissed off. I also feel guilty too though. because I believe the same thing happened to me with the same person and I wasn't brave enough to say anything. I feel like if I would have just said something she wouldn't have had to go through that ya know? I just don't know what to think at this point. any advice on how to feel a little bit better about all this?