How do I talk to her without sounding like a creep?

Try to just be friendly. Talk to her like you'd talk to anyone else (unless you feel you're creepy with most people?).

 

What kind of relationship did you have previously? Were you strangers and you asked for it because you found her attractive or was she a friend of a friend or something?

If she was a complete or almost complete stranger to you when she gave it to you, there is almost no possible way of doing it without coming off as a creep. If you at least saw each other somewhat frequently previously, like if she worked at a café you frequented for example, then I would just send her an e-mail something along the lines of:

Hey, it's FuelsMySong here, not sure if you remember me. You gave me your address like ages ago and I was going to send you an e-mail but never got around to it. I just found it again the other day and well... Better late than never, I guess? How are you doing these days? Do you still work at The Planet?

 

If you found her phone number off of google, this will seem creepy no matter what you do. Your best bet is to send her an e-mail and make it friendly, how you were thinking of her and would like to chat.

 

You could say that you've just scrolled through your old contacts or cleaned your room and found the slip of paper with her e-mail address on it (depending on how she gave it to you) and that reminded you of her so you thought it could be nice to chat a little.

If you just know her very briefly (one evening in the same club resulting in her giving you her e-mail or something) then the approach listed above would seem creepy. You could simply write to this mail stating that it was in your contacts and you did not know who she was thus prompting this e-mail so you were just checking whom it belonged to. With a little luck you might be able to let that become a frequent exchange of mail.

If you are exchanging mails on a frequent basis you should probably ask for her number so you won't accidentally reveal that you have got it already.

Also do remember that three years are an incredibly long time. That and the strength of admiration you have for her from a distance will probably lead to disappointment since she is probably not the same person you imagine or remember her to be. Just keep that in mind.

 

Ok, I think that makes it even more awkward/creepy. Sorry to say, but I don't know how receptive she'd be to this.

 

That might even be a lot easier and a lot less creepy than if she was someone else.

Just say that you found her e-mail and then chat a little about how life is for you and how she gave you perspectives etc. (normal stuff you would write any ex teacher that you liked in a friendly way) then ask if she maybe would want to meet to catch up about life and talk about old times or something.


I apologize if i am wrong but from the facts you are giving and the way you are talking i take 2 things 1. She might not be available (as a teacher and she probably has a husband or something) 2. You are not particularly happy about your obsession with her yourself. It makes you feel like a bad person for stalking her and gets in the way of other possible relationships (again apologies if i am wrong)
If that is indeed the case i would suggest trying to meet her in person to get some kind of closure. When you meet her don't try to think about why you can't have her but about why you don't want her. Think about every bad thing about her.
I am by far not an expert but i hope it could help you.