Another unfriending, this one on FB and real life

I had yet another unfriending experience on Facebook recently. I had posted this graphic:




One of my friends got very offended and said it "smacks of prejudice" and then she unfriended me. She works on my floor at work (her name is Barbara). I've seen her in the halls a couple of times since, and she's been very cool, but she's always been a bit on the chilly side (several people on my floor are like this - not unfriendly, but just sort of brusque and reserved).

So, each month we have a lunch to celebrate the birthdays for that month, and they send around a card for each person, and everyone signs it. I got my card earlier this week (even though my birthday was last month), and, you guessed it, she didn't sign my card. I'm so surprised and disappointed - it's just so cold. And all over a stupid FB post that wasn't even very confrontational (not nearly as aggressive as the last one that caused a kerfluffle - and the person that unfriended me over that post is still friendly toward me in person).  I can't decide if I should try to talk to her. Part of me feels like just forget it, but on the other hand, it's such a little thing to lose a friend over (especially now, when I feel like I need everyone in my corner that I possibly can).