If I were you, I'd ignore it because she's really reaching by coming back after 11 months. After six months It will be up to her to prove there was a problem with the vehicle when sold to her, after its been owned for longer than six months.
she'll have to provide evidence of this to establish the condition of the vehicle when sold to her - which is unlikely to be proven if she's done a lot of miles and only spotting the issue now.
source: https://www.which.co.uk/consumer-rights/advice/the-car-i-bought-has-a-problem-what-are-my-rights-aAnMC5b0ZzJb