I'm not sure what you mean about 'obtaining the doctor's verdict'? Can you clarify that please?
It would certainly help if you could bet something from your sister's GP or consultant confirming that she has little insight into her condition. Otherwise DWP are likely to believe her viewpoint rather than yours.
However, DWP's stance is that GPs and consultants are not experts in 'disability assessment' and often do not understand either the impact a condition has on someone's daily life, or the descriptors associated with ESA/PIP. Which is why people are called for assessments despite submitting reams of medical evidence.
As Nick says, points will only be scored by linking the claimant's problems to the PIP descriptors.
Nothing on this board constitutes legal advice - always consult a professional about specific problems
The following user(s) said Thank You: SomethingsUp
Hi, by doctors verdict I mean getting her GP/ Mental hospital to provide evidence of her history and symptoms to back the why some of the tasks are difficult for the claimant.