Enjoy Your Special Day Sis! Happy Birthday Card: Your sister is your best friend, your partner in crime, your shoulder to cry on, and an ear to confide in. This sweet birthday card for a special sister is elegant, and yet still carefree - just like your relationship! Charming peonies blush in light pinks and surround the sincere birthday message. For a day of fun and happiness, send a birthday greeting to your sister that will truly delight her heart and remind her how much you care.