First rule of a moan whatever treatment you have done is to make sure you actually see the client ASAP! Then make a decision about any rectification/refund...she is probs just after her money back after having the tan for her big nioht out..spent too much money and wants a way of getting some back to last her till payday!
However, it IS possible that her skin didn't like the % of tan she was sprayed with, if that's the case then its probs the best option to refund and have done with it, apologise, explain, etc
By day 5 the tan is starting to wear off and get patchy anyway.. ask open questions,like How did you exfoliate? What did you do to mosturise the tan,etc, so the answers you get are not just yes and no..and take it from there..
Good luck and let us know how you got on..x