If you were within 6 months when you contacted them which it sounds as though you may just about be, it it actually up to the retailer in this case CND to prove the product was not faulty when it was sold so this wouldn't matter who the lamp had been in contact with or used by, that's the law, I can see CNDs point of view they don't know if this woman's a professional Etc and she could have broken it but the sales of goods act does not take this into account so therefore their views or opinions on this do not apply here. In short by law you are entitled to a refund or replacement, you need to write to them stating this, the facts and what you will do if they do not comply with the law. If you are out of the six month window it is upto you to prove the fault which could be tricky as CND could claim as the product was in this woman's hands she could have caused this fault. Is the woman you sold to registered to purchase from CND? If so they cannot say she potentially mistreated the lamp as they would happily sell her one anyway if that all makes sense.