When a person with very dark brown hair wants red and blonde highlights, is it best to strip the color off the sections that she wants red so the red will show up better or just use a 40v.d. with the red color

For best results with color personaly I would strip the color out. If not your color may not hold good, or even show up well. Make sure you condition after stripping and after color just to make sure you don't cause any damage to your hair.