OV you mofo, it's about time you show your true colours
In all honesty, I agree with what a lot of people had to say about this, however, none of us know this girl nearly as well as you did. True, maybe she did change, but coming here and posting here probably will just reiterate what you already know.
Your situation (believe it or not) is similar to how me and my ex met up as well. Although I didn't know she was into me in highschool, we both thought that we woudln't have a chance with each other and just decided not to do anything about it. Although, I didn't end up maintaining feelings for her for 4 straight years, one of her friends which was sorta my friend told me that we worked at the same mall. I ended up visiting her one day and we hit it off from there. Did she ask how I found out? NOPE!
I know you say her friends all hated you. However, I'm sure that 4 years, you are all mature enough to be civil and I'm sure there's at least one of her friends that may not have hated you that much. Despite all this, I don't think that she will freak out if you "bump" into her, because if she had feelings for you, I'm sure she knows you are not a stalker. Even if she has changed her feelings, I think she'll be more surprised more than anything. Bottom line is OV, you need to do what your heart tells you even if you think it's the scariest stupidest thing. You will feel that much better after, because everything will be more in the open. You don't have to squeal all at once as Illusional said, but don't be scared. I don't think you need to. This is my "serious" advice. Take it as you like.
Cdoc