It would depend on how the work party was set up.
Is it happening during the workday and they are letting everyone take time off to attend? If so I would probably return the gifts I got and buy one of the items she requested (and probably the smallest package they come in).
Is it happening outside of work? If so I would just give an excuse, decline the invitation, return the gifts and leave it at that.
As for showers for second (third, fourth, etc) children....we have always done them around here. However, big ticket items usually are not being given, even at the first shower. Those are usually taken care of by the grandparents before the shower even happens. Shower gifts are usually clothing, diapers, wipes and toys.