Yep, you don't know her, don't care to know her, and I highly doubt being subjected to a room filled with strangers, most of them her family and is, is something someone in your position would want to subject themselves to.

Well, the sooner the better, as far as stepping down from the bridesmaid duties, would be ideal. That way, she can make arrangements for an alternate or to just eliminate the number in her bridal party.

Do you see her, often where you work? Can always say, that plans change and that though you sincerely appreciate the offer, you are unable to be there.

I'm sure, others will have some better ways on how to express this need to not be her bridesmaid!