Bit of a joke when she should be retired with her feet up. Unfortunately these days you have to over egg the pudding to get anywhere, it’s a bit like claiming on your insurance, it’s their job to find a loophole. Do your research & be well read on the subject is always best practice, the people who process these claims look for buzz words, key indicators etc.
Your sister sounds like an absolute Warrior, so no doubt she’s been a bit too proud when filling in the forms. All she has to say is she was a bit too brief & hasty when making whatever claim she made & get that appeal in, there used to be an independent welfare advisory service that would help people, not sure if they’re around anymore, but citizens advice are