I'm just gobsmacked about this whole situation.
I'd personally be terrified of thinking about my 19 year old daughter going to another country to meet someone from the web. (Hell, I was personlly just nervous about myself meeting people off the web in the local starbucks!)
However, I would know the apron strings need to be cut and I would just make sure that she's got the best tools to make it as safe as possible- i.e. credit cards she can use, calling card/phone that worked internationally, a hotel room booked, making sure they meet in a public place, paying for a friend to go in tow with her if possible.
But to be controlling and manipulative and calling the police, etc, etc, that's appalling.
Phantomrose90, definitely check into your study abroad and BUNAC options, as these offer good ways to have you come here, spend time with your BF, and well if its study abroad its a "safe" way to do it, because you have the support system of the University.
At 19, I was hopping around the USA, but had I chosen oversees, my parents would have had no qualms about me heading oversees to backpack, etc. They'd be nervous, but would know they have to let me go. Then again, my mom was hitch hiking around at 19 years old , living the hippie lifestyle, so...
Good luck. Your mom sounds like a real piece of work.