Definition of new condition for PIP tribunal

My mother (who has limited capacity) sent in the initial form for PIP in December 17 on the basis that she had had a stroke and was previously receiving DLA. She was assessed in February 18. She was not awarded PIP.

At the time she had undiagnosed level 4 and stage 4 COPD. The GP confirmed this diagnosis in March 18.

In the PIP appeal papers (supplementary advice note PA6) it states that "this condition was not reported during the assessment or on the PIP2. No medication was reported consistent with diagnosis... indicating this is a change in her circumstances. On the basis of this a new assessment would be required"

I want to argue that this occurred because she does not manage her own health - plus as far as I am aware it is not possible to develop level 4 and stage 4 COPD in the space of a month., so this would have been an undiagnosed (not new) condition at the time of the assessment.

Please can you advise me of how to address this issue in the PIP tribunal - ideally with a legal form of words, so that this condition can be taken into account in the appeal.