Need UK Law Advice

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So, I sold this woman a 2010 VW Golf around 3 months ago.
she's done around 3000 miles in it since.
she contacted me at first claiming that the car mileage was wrong and that the car had been in a serious accident.
I know it hasn't I HPI check and also check all mileage against the national mileage register so the mileage was warranted. I explained this to her and now she has had a solicitor send me a letter claiming for a full refund, the flight she took to collect the car, fuel and all kind of other expenses.
The car is perfectly fine, the inspection she had done on the car only shows cosmetic damage and I made her fully aware the car had some damage to it on the rear and shown her extra photos before she came to view and collect/pay for the car.
She had every chance to inspect it before she paid and drove it away.
How do I respond to the solicitor letter, can i respond myself? am i fucked? do i need to pay a solicitor to respond?

I would really appreciate any advice, i'm trying to run an honest business and I really don't know what to do about this.