Money was stolen from me at a party, what now?

I had my 19th birthday at must aunts house. The family was in their rooms sleeping and my guests were outside. People came inside occasionaly to use the restroom, pass out etc. All my guests were drinking and being loud outside but not inside for my family. I walked into the house at one point in time and I saw a girl coming from the back of the house. Must aunt says she was crawling on her bedroom floor. I asked her what she was doing and she said "using" the bathroom. I ended up kicking her out my party. Moments later must aunt claims money was stolen from her. So I automaticly blamed her. This happend a week and a half ago. I came to her job last night and wanted to talk to her I did tell her that she stole the money and needs to give it back. I also said she should just quit her job cause ill be up there everyday she works. I didn't know anythink about her but her con worker is must friend. I got her phone number and her work schedule, o found out what school she goes to and all. I sent her a message telling her she has till. 4pm to give the money back. And I told her I know more about her than just her phone number. I'm asking what should I do now that was 300 dollars hone 'missing'? And will I get in trouble with the cops cause I had an underage house party with liquor? Is it worth going to the cops what will happen? And can she go to the cops saying I threatend her?