Mum of three Linda Smith – diagnosed with dementia aged 57 – has launched Alzheimer’s Society’s Cardiff Memory Walk. She joined a mini version of the walk in the city with volunteers urging people to register for the event to help the charity raise money for research and services Three thousand people took part in Cardiff Memory Walk last year – and the charity hopes even more will now sign up at memorywalk.org.uk.   Linda, of Splott, a school kitchen…