If she's so worried about others' perceptions, then she's living her life in quite a restrained way. I know it's easier said than done, but maybe instead of going to hurt/annoyed/angry/offended, maybe decide that your way of living (i.e., feeling free to breastfeed in public and not care what others think) is a much better way of living. Think about it: she has gone to quite a length (and potentially strained her r/ship with you) just to avoid the potentially negative views of some of her relatives. Wow! She needs to start living her life how she wants to and not be so wrapped up about what others may or may not think. This will affect her when/if she has children and probably won't b/f herself, b/c of her family's views. It's her hang up, not yours. I wouldn't even enter into it, just attend and go with the flow, what happens, happens. She'll be too wrapped up in the whole day to notice when you breastfeed.