At first glance, I thought it would be sufficient to sample the dark pink hair colour, and add a Solid Color layer of that colour, set it to "Color" blend mode, and paint on to the roots.
But when I tried that, it left the areas too light, and they still looked a bit obvious, you know?
So instead, I tried "Soft Light" blend mode. Do you think she'll be happy with this?
After applying it, I found I had to revisit the colour of the layer, to make it pinker.