I am shocked that my stepdaughter asked my husband to make her a baby blanket for her first child.?

Don't show up. This really isn't your responsibility or your duty to do, you are not her mother, you are someone who fell in love with her dad, married him and wants a life with him. Yes, you do need to get along but that doesn't mean you need to be friends if apparently, she doesn't like you. Don't be the pushover here. State loud and clear that you will not be manipulated. Don't show up at her shower and don't make the quilt.