To be honest, I don't think she was implying that Blake Fielder Civil has achieved as much in his life as Nelson Mandela, but she did compare him to the former South African president at his 90th birthday celebrations this year, according to Gordon Brown. Whether he can be trusted or not, I'm not so sure, he is, after all, a politician.
Anyway, according to The Sun, Brown said: "As he [Mandela] looked at the concert I had this responsibility of explaining to him, as she came on stage, who Amy Winehouse was. And so I was, um, it took a bit of time to tell the full story. Then Amy Winehouse was saying to her friends, 'You know, Nelson Mandela and my husband have a great deal in common - both of them have spent a great deal of time in prison'. And then when people were singing at the end that great song, 'Free Nelson Mandela', she was actually singing, 'free Blakey my fella'".
Of course, Mandela's 27 years in prison was all to do with fighting apartheid and associated heroics. Fielder-Civil's 27 months is for GBH and perverting the course of justice.