What you say here is true. But, more to the point, it appears to be 100% irrelevant. If this woman was someone who "truly appreciates originality," she wouldn't be interested in repainting in the first place.

Unless there is more to this story than the OP and we have been given, she is not a collector. She has had the bike since it was new, has ridden and loved the heck out of it, and wants to keep on doing so (would that all nice bikes were so fortunate). Let her paint the damn thing if she wants. It's her bike, not ours. To carry on the art analogy, this is adding trees or clouds or more sea foam to a Thomas Kincaid, not painting a moustache on the Mona Lisa.

I do agree with the suggestions of doing a polish job on a portion of the frame to see if that satisfies her, not because of any inherent desire to keep it "all original," but because it may be a lower-cost way to get the lady what she wants.