Contact the insurer and advise that you accept payment on a "without prejudice basis" only (this is if the vehicle is definitely a total loss, i.e the repair costs are more than the car). Advise the insurer that you wish to raise a complaint and dispute the market value. Ask them to provide screen prints of both Glass Guide and CAP guide showing how they valued her car. Then obtain the same your self from another independent source (ask a nice car dealer). You can always if you wish not cash the cheque. I do sometimes recommend this if it may be possible to get the car repaired.