Between now and Monday get a loose leaf notebook. You need to documet everybody you talk to about your sister, every contact and resource you can find, and keep a written record of all paperwork you recieve, as well as all roadblocks you run into. Be concise, but very clear in explanations. Make no accusations in this book. Start with the phone contact with the police chief- who made the call, what she was told, date etc.
Pick up some file folders to keep the paperwork in. And I would suggest a portable file holder thingy too, so you can keep all of the files together.
Another suggestion- make copies of every piece of paper you recieve and give a copy to someone unrelated to you, quietly.