There are 3 different things considered in PIP: physical limitations, mental health requiring prompting, or cognitive limitations requiring support.
Physical: mainly activities 1, 4, 5, 6, 12
Mental: activities 1, 2, 3, 4, 6, 9, 10, 11
Cognitive: mainly activities 1, 3, 7, 8, 9, 10, 11
To back up physical limitations: GP appointments, pain team, prescriptions, specialist appointments/referrals, scans, x-rays, official diagnosis, doses of pain relief, when pain medications were last reviewed
To back up mental health problems: GP appointments, medications, therapy, community mental health nurses, psychiatrists, dietitians, tests to diagnose, official diagnosis with ongoing support.
To back cognitive limitations: specialist school, official diagnosis of either a learning disability, brain damage or impairment, dementia etc, professional support, memory tests/clinic, neurologist report/letter.
Not all, but just some of these depending on the type of condition you are claiming for. Bare in mind, the assessment alone is not enough to prove disability- anyone can claim they have one- if the degree of disability is significant there will be some of this evidence available and you should submit letters from those professionals. There are, of course, people who don’t seek help but unfortunately that will not help in the world of PIP.
The bar is high. If the person is that impaired/disabled, this input as above will be there. Submit that evidence. In short: your word is not enough, typically,