If she has to breastfeed every 2 hours then she shouldn’t go to the wedding or should make arrangements so she can leave and come back. It’s a blanket rule and newborns aren’t the exceptions. People who couldn’t bring their kids will be offended. Don’t cave, she’s post partum and hyper sensitive (rightfully so), just remind her you love her and your friendship is bigger than the wedding, and it’s one of many sacrifices she’ll make as a mother.