The singing sensation - who sold over 8.5 million copies of her debut LP `I Dreamed A Dream`, and is believed to have earned over £10 million in royalties after finding fame on `Britain`s Got Talent` - is "distressed" at having to live off the low wage, after being banned from withdrawing money from the bank or owning a credit card.
Her brother Gerry Boyle said: "Her millions are ring-fenced but Susan has no concept of money. She was extremely distressed."
Susan`s fortune is currently being looked after by her management team - consisting of Andy Stephens, Ossie Killkenny, and Susan`s lawyer niece Kirsty Foy - and she is unable to access it herself.
Susan`s financial situation is so bad, Gerry claims she has been unable to move into her new £300,000 home in Blackburn, West Lothian, because she can`t afford to buy furniture.
Gerry told the News of the World newspaper: "Susan said to me, `I`ve been told I get £300 a week because I`m a novice. I don`t have the money to go and buy the furniture.`
"She should be able to walk into a bank anywhere and say she wants £50,000 cash. That may not be advisable, but it would be her choice because it`s her money."
The `Wild Horses` singer was even forced to call an emergency meeting on June 17 to discuss her financial troubles and is concerned this means her career could be coming to an end.
Gerry has now pleaded for music mogul Simon Cowell - who owns her label SyCo and was a `Britain`s Got Talent` judge - to reassure Susan her record deal isn`t under threat.
He said: "Susan`s under the impression that her management can take her career away. Obviously that`s not the case. But I`ve asked for someone Susan trusts at SyCo - even Simon himself - to simply confirm she will not lose her contract.
"She should be riding high, developing her career, travelling the world. She shouldn`t be worried about money when she has millions in the bank."
A SyCo spokesperson said: "Finances are handled directly between an artist and their management, therefore we do not comment on such matters."