After reading the above responses, I'm surprised no one has looked at it from her perspective.
For example, thirty years ago, she dropped you because you were "needy and clingy." Now, just suppose you do happen to get in touch with her again. What do you think her reaction might be? Maybe..."Oh no...he hasn't let go after thirty years. He's still needy and clingy." Probably won't be a turn on for her.
In reality, the fact that you're still thinking about her just proves her point. You're still "clingy."
I certainly don't want to throw ice water on your dreams, but just a thought from maybe the way she might look at it.
Re needy and clingy, or being a weirdo, it's not like the OP's been stalking her for 30 years. Say he reconnects, and she says not interested, and he leaves it at that. Where's the harm?
And, could be, she has been through relationships in which no one was needy and clingy, and after 30 years on the odometer she'd like a little cling and need in a relationship.
(My sister once remarked, not unkindly, of my wife and me that we are like velcro. We are always together. We've always been this way. Needy and clingy, I suppose, compared to some/most couples, but, hey! It works for us.)
As I said, could be, probably likely, the OP will be disappointed or embarrassed, but is that such a hard thing to bear? And the gal, even if she is still not interested, rather than being unhappy at the intrusion, will maybe get a small morale boost thinking, "After all these years, he still thinks of me!" People, men and women, like to be liked.
My opinion is that too often in life we don't take chances, risks, for fear of failure, or out of worry about what others will think of us.
My view is take the risk. So what if you fall flat on your face occasionally? We're all gonna be gone soon enough and shortly thereafter no one, except a rapidly dwindling few, is even gonna remember our names..
So if there's a chance at a romance in your life that might make you happy, go for it.
And posts 2, 19 and 23 show that a reconnection can work out.