NTA - The love of art should be separated from the artist sometimes, and Harry Potter is definitely one of those cases. While JKR deserves whatever Kelly can throw at her, the story does not. You protected your friend, who is important to you. And this story is important to them. Your bridal party should be able to express themselves in their body art, especially when that's something you and your husband celebrate! It's your day, you should be able to celebrate it how you want.

You knew your audience - you knew how they would take it. A joke is only funny when both parties laugh. A judgement can't really be made unless we know their reaction