Well personally I cant understand it (probably because Cheyanne is bottle fed) but IMO its not for anyone to understand, just respect. No one has to understand why you choose to parent how you do, but I'll be damned if they don't respect it, KWIM?
September is a long time away, maybe by that time you will have changed your mind, or she will develop different sleeping habits....I agree with not wanting to take a baby in a bar. I had some friend go to a benifit banquet this weekend in a bar and they called begging me to go. I don't care how classy this banquet was, it was still in a bar and although im about as redneck as the day is long I can't really bring myself to take her to a damn bar. I went to a bar when I was 8 months pregnant and felt so damn tacky. Just my personal preferances and decisions though.
I guess the only advice I have is to go with the flow and when September gets a little bit closer review the situation and try to decide then. And let your friend know that you value your parenting decisions over her bridezilla needs. (Not trying to make her out to be a bridezilla, but IMO if she doesn't come to respect your decisions and still wants to pressure you into doing something you don't want to do just to make her happy then that will be very bridezilla.)