I would probably take a social engineering approach to this problem- if you knew her high school and approximate age you could probably find someone who was in that class who would know her pretty easily. At that point it's just a matter of either tricking them into identifying the photo or just straight-up asking them.

Or scrolling thru a classmates friends list on Facebook.

And then scrolling thru all the friends lists of all their friends on Facebook.

(Especially if they have nicely sorted their friends into "High School" friends.)

Twitter lets you do the same thing.

I've seen entire classes all "Friend" and "Follow" each other.

They knew what high school she went to (I just found out), but probably didn't know exactly how old she was.

There are no digital yearbooks from the high school. I checked