bathyboots
If your mum paid by credit card and the amount was £100 or over, the credit card company may be able to help.
Your mums contract is with B&Q and under the Sale of Good act 1979 she should be given a refund by them, but it depends on what time has passed between the sale date and date the door was found faulty. These are the key facts in bold.
Wherever goods are bought they must "conform to contract". This means they must be as described, fit for purpose and of satisfactory quality (i.e. not inherently faulty at the time of sale).
• Goods are of satisfactory quality if they reach the standard that a reasonable person would regard as satisfactory, taking into account the price and any description.
• Aspects of quality include fitness for purpose, freedom from minor defects, appearance and finish, durability and safety.
• It is the seller, not the manufacturer, who is responsible if goods do not conform to contract.
May I suggest that you contact Consumer Direct with full information on 08454 040506. See http://www.consumerdirect.gov.uk/
Huckster