I and all my co worker's (15 total) were invited to a bridal shower for a co worker I don't know well or am friends with. I am not invited to the wedding.
I do not plan on attending. I would attend if I loved this person, (that's how I feel about weddings) however I don't know them well. Bide is twenty something I am fifty seven. By the way my niece is giving the shower.
There is no compelling reason to accept an invitation to the shower of a co-worker unless your position at the company demands it. Otherwise, this is a personal decision. Also, not being invited to the wedding minimizes your obligation, if any.
I do not know your relationship with your niece, however. If she requests you attend (perhaps to help her) then you must include this in the equation when reaching your solution.