If I just posted a Happy Birthday to someone, on FB, and referred to them by something I meant for someone else, should I explain myself or just let it go?

I saw, in my FB feed, that it was someone’s birthday. I have two FB friends with the same first name. One of them used to be my babysitter a long, long time ago. I wrote “Happy Birthday to my favorite babysitter” but the birthday was for the woman who was never my babysitter. We’re distant friends thru our relatives. She’s probably going to be a bit confused as to why I am calling her my favorite babysitter.

Should I pm her and explain or just let it go? It seems like it would sound cumbersome to explain it, but on the other hand I don’t want to make her wonder what I meant.