Solid approach.

Thats your in to approach her again.

I wouldn't do it at her work, I don't know, thats weird.

Since you have talked to her 2 other times, wherever that was, just do that same thing.

This time, Tell her how sorry you were and how ridiciolous you feel- tell her its been really bugging you that you do not know her name - and then go from there.

TELLING her it's been bothering you that you do not know her name will tell her automatically that you have thought about her and she made a clear impact.