Lucy Prentice has been her mother's carer since she was 11 years old.
But now she has quit her college studies in Carmarthenshire after two years because she would lose her £64.60 a week Carers Allowance.
The rules state she cannot study more than 21 hours a week - and still get the financial support.
The Department for Work and Pensions (DWP) said it recognised the importance of carers maintaining links with education.
Lucy, 20, has joined a campaign to call for a change in the law and how it affects young carers.
Her mother Patricia, 50, has had mobility problems since suffering a brain aneurysm. She also experiences dizzy spells and severe anxiety.
As well as doing all the household chores, Lucy had to help take her mother to appointments - fitted in around her studies.
But for the third year at Coleg Sir Gar in Carmarthen, she would have gone over the maximum 21 hours a week she can spend on college work and still qualify.
Her mother receives around £300 a month in benefits but the Carers Allowance is vital for paying for things like heating and helps run Lucy's car.
"It's a godsend," said Lucy. "I can buy personal hygiene items and things I need. Also we got into a pickle with heating costs and were in debt after we filled the oil tank for the central heating. The Carers' Allowance meant we could pay that off."
"My mum has a weakness on her left side so she can't stand or walk for very long so I help her. Her anxiety is very bad so she can't leave the house without me.
"I help her pay the bills, attend appointments and on bad days I'm like a counsellor."
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The rule over care allowances applies to post-16 education, including carers in sixth forms and colleges.
To be eligible, you must be over 16 and care for someone for at least 35 hours a week.
"I would love to go back to college but I can't afford to lose the money," said Lucy, who had studied business administration and switched to animal management.
She had been working towards a career in the care industry and also hopes of her own business with animal rescue.
"I worry about my future - I don't want to end up on Jobseekers Allowance," she said. "I worry I won't get a good job or earn good money. We struggle now and I don't want it to be the same in the future."
Melanie Rees-Lewis, from Carers Trust Crossroads Sir Gar, said the law needs to change.
"Young carers face enough barriers engaging with education due to their caring responsibilities as it is," she said.
"As a society, we need to remove barriers and help them advance their career and reach their full potential and have the same opportunities as other young people.
Suzy Davies Conservative social services spokeswoman and South Wales West AM, is hosting a campaign event highlighting the issue in Llanelli on Monday.
She is proposing a young adult carers grant to give young adult carers, who lose their care allowance, £60 a week to enable them to enter full time education and training.
Ms Davies is also arguing that young carers are meeting the 35-hour threshold, with what they do at weekends and even support over the phone while in college.
"Young adult carers shouldn't have to drop out of part or full time education, or apprenticeship opportunities, just because they have caring responsibilities," she said.
"Our young adult carers are true heroes, undervalued even though they keep families together and take the strain of looking after vulnerable family members."
In a statement the DWP said: "We value the vital contribution made by carers in supporting some of the most vulnerable people in society, and we recognise the importance of carers maintaining links with the education system and achieving their full potential.
"Carers can undertake up to 21 hours of supervised study per week and still receive carer's allowance. Carers in full-time education may also be eligible for other financial support through the educational maintenance system."