And it's a world I've left, for the most part. I no longer work in cubicle land, I work from home for a very small company and have no aspirations that compel me to attend many duty events.
My husband also works for a small company, but we recieved an invitation we're sitting on for the wedding of a co-worker he barely knows... and we're trying to decide if it's rude to decline. She invited us only out of duty, so perhaps she'd be quite happy if we honor the sentiment by not actually going ;~D
Every guest at a wedding COSTS. Guests who say, "No, thank you," promptly only cost the price of the invitation.
I'll bet if you decline, and then send a card with a small gift off her registration list, you will be her very favorite people!