Stacey-Ann Small assumed the identity of Rachael Davis - who died from a lung infection 31 years ago - and married and claimed government handouts in her name.
Norma Harrison said Small's actions had made the pain of losing Rachael at just 11 months old even harder to deal with.
"What she did has made the pain of what happened harder – to know she was doing all that as my daughter," said Miss Harrison, 51, of Aspley, Nottinghamshire.
"But I can't really say I hate this woman because I don't know her and she doesn't know me. She doesn't know what damage she's done."
The shocked mum was told by the police of the identity theft when the investigation into Small's activities was conducted.
"You read things in the papers about people trying to get passports under different names – but you don't expect something like this to happen to your family. It feels like nobody is safe," Miss Harrison told her local paper.
Stacey-Ann Small, an illegal immigrant from Jamaica, pocketed £20,000 in benefits she was not entitled to using Rachael's name.
The 29-year-old, who was living in Bedworth, Warwickshire, claimed jobseekers' allowance and income support.
The Coventry Telegraph reports that she assumed Rachael's identity in 2006 after picking up her birth certificate from a friend, and used the baby's ID to register the birth of her own child and to get married. She did, however, fail in her attempt to get a passport.
She has now been imprisoned for two years.