if she tries to hide it, it could be because she simply doesn’t want to bring up horrible memories which have no importance anymore. she has the right to a happy future, even if that means hiding a horrible secret which wasn’t her fault. that is between her and allah swt now.
i don’t think the girl should have to tell anyone, if she doesn’t want to. just as the guy isn’t expected to tell his future wife about his past relationships, if he doesn’t want to.