I hosted my girlfriends hens night when I was 37 weeks!! Luckily it was a nice dinner out and then ****tails and no dance on the table shenanigans!! I was meant to be bridesmaid, pregnant or with baby - turns out baby came on the day of the wedding!
I love weddings though so I think I would go either way - whether it was my close friend or not!
Clothing is hard to find but not impossible and if you get tired and have to leave early or even have a little nap somewhere -people are very forgiving when you are huge and pregnant! I went to one when I was 24 weeks - so not that big but my feet had swollen to enormous levels from 16 weeks so I had to wear thongs to the wedding and sit with my feet up half the night ! Good look but nobody minded!
Good luck!