Emily Post, where are you?

I received a wedding invitation from a co-worker! Help!

I just started this job one year ago (August 25). The gal that is getting married started just shortly before I did. We were sort of thrown together on the office Christmas gift buying, as the "new person" is assigned that glorious task (which I still say is some sort of professional hazing). But anyway, we chatted during our Christmas gift fun...and still talk when we see each other if only to say, "Thank God there are other "new people" in the office this year so we will be spared a repeat of that agony." I generally ask about her wedding plans and how she's holding up under the stress. But I wouldn't say we are friends by any means.

So Ms. Post...do I RSVP yes or no? I see advantages and disadvantages. If I say yes, I would be encouraging a friendly relationship with this co-worker by acknowledging that her wedding is important enough to me to attend. However, what if it was only a courtesy invite and she never really expected me to attend? Will I be creating a grudge...by obligating her to provide me with meal and drink on that day (when all she really expected was a gift)? I just don't know! Do I respectfully decline and risk offending her? Do I decline and send a gift? OY!