I believe Tammy is on the "ruled out" list.
Just an FYI there are two choices when dying your hair dark brown and that is cooler which would be more golden-brown and warmer would be reddish/coppery brown depending on what shade the hair is before coloring it could come out a variety of ways. She describes them as reddish-purple tones, which leads me to believe its not highlights of red or purple but likely a single dark brown(warmer)color that has built-in highlights. When you see a girl that has bright red or purple hair that has naturally dark hair to begin with she would have to bleach the hair before applying the red or purple, which fades rather quickly, and must be reapplied probably around every two weeks(depending on how often the hair is washed) if you do not reapply you would end up with bleach blonde hair, not subtle hues.
Source: I am a brunette who loves to play with hair dye.