So LordL needs a tidy phrase he can repeat over and over that won't involve JADEing to her. Something that doesn't validate her actions, which I feel like we'd be doing by saying something like "We appreciate the sentiment, but..." Maybe "We've decided that we'd rather not have a shower. <insert her protests> We do not want a shower. I know you already invited Aunt Edna but we do not want a shower and any plans involving us need to be run by us beforehand."
Is that the right degree of directness or do you think it could be softened somehow without diluting the point?
This sort of thing would really make me angry.
I think I might phrase it more like, "We decided [previously] that we didn't want to have any showers or other pre-wedding events. So, we don't want to have one at the family reunion or any other time. Also, we really don't like surprise plans, so please don't make any more for events involving us."
Or something like that. I think you should be clear that you aren't just deciding you don't want
her shower, it's that you don't want
any, and you already decided this before her idea was ever brought up. You're not specifically putting down her idea or hoping someone else makes a better offer. Actually, I don't mean that to make her feel better, I mean it to emphasize the point that if she'd
talked to you guys beforehand, you would have told her this right away, and she wouldn't have gotten all involved in planning and telling other people about it.
As a side note, I think of "We appreciate the sentiment" in the same vein as "it's the thought that counts." Sometimes, the thought isn't very nice, and
that's what I'm counting--i.e., I'm noting that you gave me a stained dishtowel and an open box of band-aids as a gift, and in the future I won't bother spending much time or effort on gifts to
you. So in this case, you can appreciate (recognize) the sentiment (of her wanting to take over your wedding). So I think you could still use that phrase, if you think it would mollify her. But if you think it would just encourage her to keep making other unauthorized plans, definitely avoid it.
And I have to agree with the others, attending the family reunion sounds like a dangerous prospect now. A shower is easy to spring on someone at a gathering, and it's hard to walk away without looking like a bad person to the (innocent) guests and making them uncomfortable. If you do attend, I would be on the alert for any signs that a shower was starting up--maybe enlist a couple of sympathetic cousins to keep an eye out for you--and skip out of the room the instant you get suspicious. Like, I would literally hide in the bathroom and then sneak out the back door if necessary, trying to avoid a scene in front of the other guests. Then she'll be the one who looks silly, announcing a shower for someone who's clearly not there.