That is possible. If Beth believed from the start that she was kidnapped, then any talk of her being seen going off with three guys would translate to "she was kidnapped by three guys". However, I believe Beth refused to think of Natalee being dead, so whatever was or wasn't said by the chaperone, I think Beth would think "kidnapping", not murder or manslaughter or negligent homicide or accidental death, etc.
I agree with that.