DD (16) dyed her hair red in lockdown with a box dye. All good. Then she got bored with it and dyed it brown (box dye). This looked good for a while but then the brown started to wear off but you can still see the red (now a gingery colour) underneath. She's done one more brown box dye since and is really fed up of the gingery colour. She wants to get back to a dark brown (a shade or two darker than her natural hair colour).
Can any hairdressers please advise? What can she do? Will she just have to wait for the red to grow out? Why doesn't it fade like the browns?