I don’t think that it’s like a Hen Party. Friends/relatives of the Bride host a party and invite women close to the Bride and Groom to participate.
In this case the party is a luncheon at a restaurant but it can be at someone’s home, etc.
The purpose of a shower is to assist the Bride fill her new home with useful objects to help her embark on her new role as a wife.
Showers may have started back in the days when girls kept a Hope Chest and lived at home until their wedding day, but the tradition still continues today.
Brides usually “register” on
Amazon and at stores that carry a lot of shower gift merchandise. That way buyers will know what she needs and wants (china, linens, small appliances, etc.) but you can also buy a different gift of you own choosing.
Work colleagues may hold a small shower at work and girlfriends may have a small “personal shower” with gifts of lingerie and sleep ware.
It’s just people pitching in to help the Bride and Groom start their life together.