The bridal shower is hosted and planned by other people, not the bride. If someone offers to host a shower for you it's fine for you to accept it but you're not owed one or entitled to one.
It's also a faux pas for immediate family to host the shower, though traditionally the MOH & bridesmaids host the shower and often the MOH is a sister so personally I've never seen an issue with it. Most showers I've been to have been hosted by a sister or a mom.
Guests are generally people that the bride is close who will also be invited to the wedding whether it's friends, family members, co-workers, etc.
Showers are also entirely optional. I didn't have a shower and I do have friends, I didn't want one.