This is a very clever idea to make life a lot easier for the bridesmaids organising the hen.
All you need to do is create a closed Facebook group and invite the guests to join. You can include the time, date and all instructions for the hen.
It's also a good way for people to post comments and get to know each other a little before the hen.
You can post all your photos to the group afterwards, without having to worry about being tagged publically. (what goes on hen stays on hen!)
It's also a lovely way to make the bride feel special and the centre of attention before the event!