Her sister must be beside herself. She no doubt kept her mouth shut because she was terrified for her sister- just talk to experts in the field, and they will tell you so- I pray for them all. Especially that young sister. If Elizabeth turns up dead, the sister will always be wondering if she had anything to do with it, or could have done something different. It will haunt this poor family for the rest of their lives. This is such a tragedy.
We don't really know if she kept her mouth shut for two hours. It might be a lie by parents and police. Its just as possible she went to parents right away and the parents don't want that to affect what the kidnapper does.