Hi Gemha, funnily enough i've just had a very long conversation with my mother-in-law who rang to invite us out for dinner at the weekend....I explained that I wasn't eating because I needed to lost a serious amount of weight prior to my surgery in November and then proceeded to get a lecture as to how that would mean that I was too weak to face the op, how bad this diet was and the icing on the cake "but you can just have a salad"! Whilst resisting then urge to scream I patiently explained that I'd lost 8lbs this week which, if I had been following a conventional diet, ie WW! Would probably have taken me a month and by which time I might well have given up! Eventually I think that she understood that I have to do this and a diet of salads just won't cut the mustard!
My tip is avoid eating out at if at all possible but, having done LT back in 1997 and having lost about 49lbs, I know that's not possible so explain what you're trying to do and why and if your family and friends love you and want what's best for you they'll understand. If you can go along and just drink water then good for you, but if not, just don't go!
Is the wedding reception a sit-down meal or a finger buffet? If the latter and your resolve is good then you should be ok, can you find someone to keep you on the dancefloor? Weddings are guaranteed to have 100% cheesy music that you can dance to and maybe use a few extra calories too?
Good luck, let us know how you get on...