How do i reach out to a girl we had a thing going when its been over a decade?

How do i reach out to a girl that we had a thing going through social media when it's been over 12 years? Me and her had a thing going all through high school, she was older so she graduated first and lost contact. How do i reach out to her without it being awkward when its been that long? I dont care what direction things go as long as i can get closure either way about the one that got away and what if. I know at one point she was trying to reach out as my friends would tell she would attend their parties all the time maybe seeing if i attended also which I didn't unfortunately.