Hey - you should report this theft as it is a crime. I would ask your mom and dad to help you out on this one, as I am assuming you are also still in highschool and are not an adult yet.
Here is a link to the Vancouver Police Department online crime reporting system:

. I believe it will take you through a step-by-step process of how to report what happened today. I would recommend writing everything down so that it is clear in your mind before you start filling in this online form. Also, having a written record will help you once the police call you to discuss what happened. I would also recommend saving your emails/voicemails, etc. and even transcribing those (writing them out).
Any theft is a crime, and whether this girl took the clothes and had someone else steal them from her is irrelevant right now. The police will do their best to get to the bottom of it and locate the clothes. If I had to guess, this girl probably has them at her house...
I would file the claim tonight, with the help of a trusted adult. That way, the police can start working on this sooner rather than later and will be more likely to find out what happened.