Should surprise the Bride-to-be with a shower even if she has requested no to have one?

WOW, that is a tough question! I think that it all depends on the person your sister is. What I mean for example is say your best friends b-day is coming up and she keeps bringing up the fact she doesn't want you to throw her a party because she doesn't want you to "go all out". But then when her day gets here and you didn't throw her one she gets all mad about it, saying that you should not have listened to her, my best friend would do that! Anyways- I would throw her some type of shower if I were you, let the guests know that gifts are optional but their attendance is requested just to let the Bride and groom know that they are loved and cherished. Maybe throw a them a BBQ (if that's something you guys like to do) and invite everyone that is invited to the wedding. Just tell them to bring their favorite dish, and explain to them the bride and groom's wishes (about the no gift thing). Then if they still choose to bring gifts then it will be on them. I do not think that your sister will be mad at you not following her wishes, but she will be glad that you didn't go all out and do something huge and unwanted behind her back.