Add extra fun and celebration by sending perfect birthday wishes to your sister-in-law, on her day. Whether you gained a new sister via your marriage on your bro’s marriage, or the change created a brand new relationship with your family. Your sister-in-law mightn’t have been born in your family, but she is a vital member of your family dynamic. Use this perfect cupcake wish card with heartfelt lines for your sister-in-law to show that you love her.