Compromise and paint it the color she wants to paint it.
BWHAHAHA!!!
I laughed a little too hard at this!
Has she ever painted/finished a rocket before? To what level of detail?
One option is to lead her to a thread here that shows how much of a PITA it can be to achieve a nice finish.
Another option is paint it yourself. Take weeks with curing, sanding, spraying, repeat, repeat....repeat. Maybe she'll rethink it.
And another is let her paint it and just leave it at that.
Come up with a scheme that incorporates a significant amount of black. Mask off the black areas so after all is said and done all of the black will be bare fiberglass. Then clear coat, especially if you'll be wet sanding, so you don't inadvertently, uhm, fade to black.
Examples to be left black:
Roll patterns
Name
Striping
Flames
Nose cone
Fins
I've always liked yellow, "alien" green, or orange with black. But really most anything goes with black. I've done Carbon red with flat black (turned out REALLY nice), Emerald green metallic, blue, and purple with black as well. All look good.
My near-wife has mentioned twice now that she wants to build a rocket. I picked up an Estes Executioner to give her for Christmas. We'll see how this goes. It may be a good thing the doctor put me on beta blockers.
All else aside...you know what to do. If not, she'll set ya straight.