Her email isn't polite in the slightest. She sounds very demanding and I agree sounds like she is being a bridezilla. As a Christian I hate hearing of ppl being discriminated against in Church. It is God's church and in my eyes God created our boobs for our babies and I guarantee he would encourage women to breastfeed wherever and whenever their babies needed to be fed. I probably wouldn't go if it were me or I would go but not discuss it with her any further and feed in the day how I normally feed. Like you said, you've bought a special dress for the day so no one will even know you're feeding anyway. The bride will be too busy to notice so just do what you do and feed bub when he needs to regardless of whether you're in the Church or reception!