It's probably just colour left on the surface of the hair. As we know red is one of the larger colour molecules that is the hardest to get right in the hair. Some of the colour molecules are probably sat either on or just below the cuticles and when she's shampooing (opening the cuticle) colour is seeping out. It's so important to use an anti oxidising shampoo and conditioner to finish the colouring process, especially with vivid colours. If she's noticing colour transfer when she towel dries her hair she's obviously using a light coloured towel, which anybody with and ounce of common sense would know is a school kid error!
No reason to refund whatsoever. If she washed her towels appropriately the colour transfer will come out, because its no longer oxidative, and is only surface colour, which has been diluted with a lot of water and shampoo etc....
For future reference make sure when doing vibrant colours, you insist on using a dark /colourful towel and always rinse the hair really well (until the water runs clear) definitely use anti oxi products too.