The fact that many/most Universities don't read PSs is irrelevant. Some do. Warwick does for its over-subscribed courses. I have linked their guidance above. OPs DD is applying to Warwick or a popular course.
I always find this MN idea that once a child is 18 they are adults so need to do everything themselves, rather odd. I see the various challenges: writing PS, renting first flat, etc as learning/mentoring opportunities. I showed DD how to check the inventory and sort out utilities on her first flat. I have not needed to do so since. In the same way that I would help a friend if they asked me for help with something. I have recently been involved in mentoring Ukrainian tenants/refugees about a whole range of things, from registering with a GP, through to the need for thick curtains and draught excluders. Help has included research into how to get equivalence for their qualifications and suggesting a major restructuring of their CVs.
If I am happy to hand hold others in instances where my experience is greater than theirs, I don't see why I should not do the same for a DC. It is a useful learning experience. What I tried to do was get DD on from the blank sheet of paper in small steps, by suggesting what she should research and how she might structure. It meant that when she came to apply for an intercalation degree, she was confident enough to write a successful application on her own.
Both DC were applying to oversubscribed courses with 4xA* predictions, predictions that matched their AS results. I never saw DS' PS, but he received three rejections, including from Warwick and UCL. I asked him more recently what he thought had gone wrong, and he confirmed that in retrospect his PS was not that good. DD was applying for medicine, but with a weak UCAT and too ill to prepare for BMAT. She needed to apply to medical schools that prioritised PS and academic results. Hence the careful approach to the PS outlined above.
It was very much her PS, and she had no problem at interview talking about any of the content. I think at the time Bristol received 17 applications for every place (it was the last year that Bristol did not use aptitude tests). Understanding how initial scoring might happen and that the need to tick every box is important, is probably not something a 17 year old knows.
Job/internship applications can be expected to be way more competitive. Writing a PS is a good opportunity to learn how organisations are likely to apply an initial filter. If you do not have recent experience of applying for a large or public sector organisation, it is probably worth asking a friend or neighbour, with that experience, to read through, with a printout of the University CV guidance.
In terms of school help, DDs private school were very careful to limit to comments rather than suggestions. So lots of "expand" or "needs to be clearer" but no suggested wording. No doubt some used professional help but I am not sure that helped. DD read a friend's PS which was very polished but had little content (he did not have a lot of extra-curricular and if the truth be known was probably applying to read medicine because both parents were doctors and it was assumed he would). He had great grades but only got one interview and no offers. I would expect admissions officers who read PSs can spot those that read like a 17 year old has written it, as opposed to one written by a professional, even it they have received suggestions/mentoring from school or family.
(Sorry it sounds a bit ranty. The message to OP is that her DD should give the PS her best shot. It is not easy, but it is a good learning experience, and Warwick has a great history course.)