Sheryvone Brooks, aged 20, was caught on CCTV taking £30 from the Evelyn Nicholson, Wolverhampton Crown Court was told.
The camera had been installed in the kitchen of the house in Stourbridge where the money was kept just six days earlier because her family fear cash was going missing, said Mr Geoffrey Dann, prosecuting.
He explained: "The footage shows the defendant opened a drawer, take out the purse and put the money in her tracksuit top."
Brooks, from Foxmeadow Close, Sedgley – one of a team of carers from Gateway Heath and Social Care, Dudley, looking after Mrs Nicholson – pleaded guilty to a single offence of theft involving £30.
Mr Jason Aris, defending, declared: "Nothing I can say could justify her actions. It was a very unpleasant offence and the shame she feels is all consuming."
Brooks, who had no previous convictions, fought back tears as she was sent to a young offenders institution for 26 weeks.
Judge Martin Walsh told her: "This was a mean and despicable offence.
"You stole the purse of an 85 year old woman who you were employed to care for.
"It is not the value of the property involved that is important in this case. It is the nature of the relationship between you and the elderly person you were required to provide care for. This was a gross breach of trust."
The judge added: "The sentence is designed not only to punish you but to deter others. People in the profession you were part of must understand that offending of this kind committed against elderly people in their own home will result in the offender being sent into custody."
The family of Mrs Nicholson applauded the decision to lock up her thieving carer.
Mr Robert Smith, aged 65, and one of her seven children – she also has 16 grandchildren, 30 great grandchildren, and 11 great great grandchildren – said after the case: "I am happy she has been sent down.
"She had worked with my mother for six months and was one of several carers who make four visits a day.
"My mom cannot walk or stand without the assistance of the carers. They allow her to stop at her own home which is what both she and the family want.
"I want to make it clear that the other carer working with her that day had nothing at all to do with this theft."
Mr Smith continued: "We had noticed about £200 had gone missing over the two weeks up to Christmas. I am responsible for my mom's finances. I put the money in her purse each week and the purse in the drawer.
"My mom worked damn hard all her life and did not deserve something like this to happen to her but Gateway have been very good about this and are still caring for her.
"We have tried to keep as much of this from mom as possible, she had to go into respite care for a couple of weeks after it had happened because it really knocked her about, but she still thinks the world of all the other carers involved in looking after her."