I'd wear it. It's not bridal unless the it's a third-time bride on a soap opera. With the instructions you've been given, I'd say a strong no to anything with lace or tulle, extensive beading or embroidery. After that, the only thing that makes this "bridal" is that it's 1) white, and 2) floor length. She's demanding white and floor length with a black tie all women wear white instruction.
If the bride is going to be bothered by this dress being too bridal, I'm sure there will be 15 women ahead of you in the line of fire.