Cathy Mohan, who said she has a mild learning disability, challenged the PM as she was campaigning in Abingdon, Oxfordshire.
She stopped Mrs May in the town’s market, telling her the “fat cats get the money and us lot get nothing”.
She added: “I’m talking about everybody. Everybody who’s got mental health – and everybody who’s got learning disabilities – I want them not to have their money taken away from them and being crippled.”
Many people say the move from disability allowances to PIPs (Personal Independence Payment) has left them struggling to get by.
“I want my disability living allowance to come back, not have PIPs and get nothing. I can’t live on £100 a month,” Ms Mohan said.
“Who’s going to help me?” she pleaded.
The exchange happened as the PM was walking through a market with the constituency’s Tory candidate, Nicola Blackwood.
Mrs May tried to reassure Ms Mohan, telling her: “Nicola can help you specifically. What I can do is ensure we’re giving more help to people with mental health and learning disabilities.
“And that’s exactly what we’ve done, we made an announcement the other day… When we look at the help we give to people with any disability, it’s particularly we focus on those who are most in need.”
PIPs payments currently vary from around £22 a week to £141.10, and depends on the severity of a person’s disability.
When they were being introduced, the Institute for Fiscal Studies predicted 370,000 people would be affected, leaving them each an average of £3,500 worse off.