red highlights on red hair...

Hi, and welcome to the forum! I am not a pro, so I may not be the best one to answer your question. I do not usually do highlights on myself. I know people do them with foils if they want big chunks of highlights, or they use a cap with holes in it and pull small pieces of hair through it for small all over highlights. I used to highlight a small amount of hair around my face, all I did for this was keep this hair separate from the rest and do only this hair. (I used a plastic claw clip to hold it in a coil away from the rest.)

I know that the pros do it the way you describe, putting the color on, then removing it from the highlights - it sounds like more steps this way, but I can see why they would, it would be harder to keep a whole head of highlights separate while doing the base color. It is a very complicated process. She may have used ColorFix or Color Oops to remove the base color, then do the highlights. if you use that, you will have to rinse VERY well to remove the color.

Since you are doing this yourself, you should do test strands to make sure the colors will come out how you want. The more times you dye hair, the more porous it becomes, and this can change how it comes out even if you use the same colors.