the cost of having an awesome email address

My email address is the real life equivalent of lucy at gmail.com so I get quite a bit of mail that's meant for other Lucys who presumably forget that they had to add a number or something to their username. Two years ago I got an email from Rosemary. It obviously wasn't spam so I replied to say I wasn't the Lucy she was aiming for and to please remove me from her address book. She wrote back "Lucy, it's me Rosemary", because apparently I might just ask everyone to stop emailing me without checking if I recognise their name. I wrote back again, asking if she was sure she knew me, because I was fairly certain I didn't know anyone called Rosemary and she never replied.

Today, Rosemary tried to friend me on facebook. She also commented on my profile pic, which makes me think (a) I missed a privacy option somewhere and (b) either I'm going senile and have forgotten ever meeting this person or she is, since she managed to look at my picture and not realise that she's never met me. I'm pretty sure it's her, but should I send her a message again to ask how she thinks she knows me?