Don't do it, I was in the same situation. Her bday was coming and I already ordered a bouquet for her, at the time when we broke up I couldn't cancel the order so she received them. She didn't even care, she just remided me why I started to hate her and why I started to hang around with an another girl who is now my girlfriend. Now when I think back I tell myself I could spend that money on a fine hand rolled premium Cuban cigar.
What you need to do is to forget about her, sending her that card will only slow you down in the process of healing because you're going to think about her and what she thinks about the card. Keep NC and move on, one day you'll find someone who deserves that card!