re: What age to let daughters get her ears pierced?

I think you are correct and this is a slippery psychological slope as a practice in general. This is obviously something your wife wants herself and for show, the baby is clueless. Before she starts this vicarious exhibition and public display through her child... first of all, does she fully understand exactly why she wants to do this and where will it stop? You may horrified to see how far this can actually go.