I don't honestly see what is the problem with the shower? I think it would be nice of you to go, and to go with an open mind and heart. Any baby deserves celebrating, whether it's with beer, champagne or orange juice.

If you aren't prepared to go to her shower, then honestly, I don't think you have a relationship with her, so I'd forget trying to 'educate' her. If she makes choices that are different to yours, her baby will still (presumably) be loved and cherished.
If you truly want to be part of the life of your niece and want the best for her, then you should go to the shower with a lovely gift, which could include an AP book if you wish, but should not be designed to 'educate'. Gifts should be given from the heart, not as a means to try to persuade the other person to agree with your own opinions, imo.
I can understand that you don't want a relationship with your brother, but I think you need to make a choice - whether to maintain a relationship with your SIL for its own sake, or whether you are just too different to get along, and let it drop.