Audrey Barnett worked for the DWP for 15 years until she was granted medical retirement with multiple conditions in 2008, she told Holyrood's Welfare Reform Committee.
She has 12 conditions including degenerative brain disease multiple sclerosis (MS) and immune disease lupus which make work "extremely difficult", according to her GP.
When told by the DWP to prepare herself to return to work, she asked her local MP, Chief Secretary to the Treasury Danny Alexander, for help and received six pages of "waffle" from his Cabinet colleague Iain Duncan Smith, she said.
The UK Work and Pensions Secretary wrote that people with MS need to be reassessed "because there are new treatments coming on", she said.
Ms Barnett said: "If there's a new treatment that can cure me, can I have it please.
"I had a meeting with Danny Alexander, the MP for our area, and he contacted Iain Duncan Smith who sent me back a six-page letter waffling on and it looks like there's no intention of changing anything.
"He's justifying what they're doing, saying people with MS have to be regularly reviewed because there are new treatments coming on.
"I've spent years on the other side working for the DWP and now that I need them I have to fight for everything. I just feel let down and I feel like they're treating me like a scrounger.
"I fully understand that benefit tests have to be done but if you get to the stage where a chronic, progressive illness has caused you to have to give up your career, then common sense should come into it and you should be put into the support group and left alone."
Mental health support worker Donald McKenzie, from Support in Mind Scotland, said he is surprised a DWP assessment centre in Edinburgh did not get its windows smashed because of the distress its reassessment caused one of his users.
"Somebody had won a tribunal and were awarded employment support allowance (ESA) for a year - a year after the original assessment date.
"So they'd only just got their back money and they were sent a new questionnaire.
"That person went ballistic and it surprised me that they didn't go straight round to York Place and kick the windows in.
"They were so distressed, so angry, so upset and I was as well because we had just gone through all that stuff at tribunal, were awarded ESA and then a few weeks later got the forms to start all over again."
The committee also heard from a polio survivor whose benefits were cut for a year but later given back to her with backpay.
Rosena McKeown, 54, also said she had "no choice but to pay the bedroom tax" when her application to move from a three-bedroom flat to a smaller property was delayed.
A DWP spokeswoman said: "The work capability assessment was introduced in 2008 by the previous government and we have made, and continue to make, significant improvements to the process since then.
"We think it's right to look at what work people can do with the right support rather than just write people off out of work sickness benefits as sometimes happened in the past.
"There is also strong evidence that working can be beneficial for many people who have a health condition and many disability organisations, including the MS Society themselves, point out many people continue to work for many years after their diagnosis."