I am good with some coordination!!!
I do think that with the black tuxes being the biggest color factor, that blue would really stand out / clash.
And, the bride was probably going for something more neutral to coordinate.
I can't see how beige would ever stand out. ( I believe that is what is behind the "MIL wears beige" thing!!!!!)
OP, I have a suggestion.... to go with the color that I am thinking is a dark burgundy, how about a lighter color in that color family???
And, I would still be happy if I could find a nice dress that flatters, in a beige color.
Here is a nice dress in an interesting color. Called Petal.
It does have a lot of sequins.. and on this website, they only have two small sizes. But, just some different ideas to consider...
macys.com/shop/product/calvin-klein-draped-back-sequined-gown?ID=2916270&CategoryID=203153&swatchColor=Petal&swatchColor=Petal#fn=COLOR%3DPink%3B%3BPurple%26SIZE%3D%26sp%3D1%26spc%3D805%26ruleId%3D78|BOOST ATTRIBUTE%26searchPass%3DmatchNone%26slotId%3D3
And, here is one in a color called Rose Gold.
macys.com/shop/product/nightway-sequined-lace-slit-gown?ID=6160927&CategoryID=203153&swatchColor=Rose%2FGold#fn=COLOR%3DPink%3B%3BPurple%26SIZE%3D%26sp%3D1%26spc%3D151%26ruleId%3D78|BOOST ATTRIBUTE%26searchPass%3DmatchNone%26slotId%3D51