She COULD get a wig. But I used green in my hair once, and let it stay for a day or two, and I had very light staining. You couldn't notice though, because my hair is black.
Tell her to do a HIDDEN strand test, mark it with a bobby pin [so she can find it later], and go on about the day. Then wash it off, and see if it stains. If not, yay! If it does...wig it out.