Heather Raghavjee, whose husband Dr Pox Raghavjee was killed in a carjacking three years ago, said her heart went out to "the young lad".
British newlywed Mr Dewani is accused of having hired a hitman to kill his bride Anni on their South African honeymoon, and has also been linked to the murder of Dr Raghavjee.
South African national commissioner Bheki Cele has said police are investigating a link between the wealthy businessman and the 2007 murder.
Publicist Max Clifford, who represents Mr Dewani, has dismissed the possibility his client was implicated in either murder.
Yesterday he issued a statement from Mrs Raghavjee, which said: "I am very upset myself, and particularly for Shrien and his family, for the awful accusations that have emerged from South Africa, concerning the murder of my husband three years ago.
"There is absolutely no substance in these allegations, and my heart goes out to the young lad."
Mr Clifford has said Mr Dewani, from Westbury-on-Trym, Bristol, met Mrs Raghavjee in South Africa after the murder.
But he said they had never previously met and Mrs Raghavjee had made the journey at the request of her daughter-in-law, Alvita Raghavjee, who lives in the Bristol area and knows the Dewani family.