Should step mother be invited to office bridal shower if mother is?

This is best determined by the bride. If she wants her there, then yes. If not, then no. It is not rude to not invite a person if it is forseen that this would provide displeasure. And it is never rude to refuse to invite a person to a shower, or any other event, for any reason. It may be wrong to tell a person why,but a shower should be pleasurable, first and foremost.