I told a girl I've known forever that I love her and were not even dating and she won't talk to me now. What should I do?

What result do you want?

Well, she may have just thought of you as a friend and now she feels pressured. Maybe you should just not talk and give her space to think about how she wants to react. Talking to her may just scare her farther away.

Have you talked to her at all since you told her? What was her respons when you told her?

She might just feel a little pressured, maybe she just sees you as a friend and now she doesn't want to lead you on/give you the wrong impression, or she might need time to digest the info, before talking with you again...

Like you said, you've known this girl for a really long time. So she probably never thought of you in that way, so let her reflect on what you said first.

However, there is another side to this story. She might not feel the same way about you and she's ignoring you so that you can recover.

But let's just wait and see. Be patient.

Tell her that you didn't mean to make her feel pressured or make her back off.
Let her know that you are cool with things where they were. That you didn't mean to jeopardize your friendship by telling her that you love qualities about her that you find outstanding and amazing.