It's your machine. If you want to repaint it, please take a picture of her current look to commemorate the hours of sewing done on it. Loved machines quite often are 'used' looking. Pristine machines may not have had the luxury of being well loved. Personally, I can see black with pretty roses, but a bright color and roses might be a little much for a full sized dignified machine, IMO. Again, it's your machine. Do what makes you smile after you photograph her.
Now I'm ducking - this may not be the popular opinion.
