You didn't say if you are in the wedding or not. I was in a wedding when my son was 3 months old. The dress was strapless, and made the whole thing very difficult. I talked to someone in the offices before the wedding to see if it was possible to use a private space after the ceremony. She offered her office, as I had to get myself out of the dress and bra to nurse and didn't want to leak on the dress. I was a bit engorged after the ceremony, but fed as close to the beginning of the ceremony as possible, then at the reception, waited for the toasts, etc, and then went running to the office to nurse. I brought my husband along to help with the dress and hold the baby as necessary. Yes, I was a little full, but didn't show leakage due to some awesome washable breastpads (PuffyMondaes.com) that I changed after feeding, just to make sure.
If you aren't in the wedding, there are some nursing friendly dresses out there, and a hooter hider should be plenty to stay modest. If you aren't comfortable with that, find a more private place and/or ask your friend if she would have a problem with your nursing, or where you might find a place to do so. If you opt for the skirt/top route, there is also a product called Blush topless shirts that are amazing for modesty (don't show that belly while nursing) that I can't live without. Good luck and have fun.