I'd written a reply and it's just refreshed 
. Apologies if the second attempt sounds abrupt.
I hope you didn't think that I was disbelieving your DD. I just wanted to give you as her mum a frame of reference of what's typical.
The accent situation could be a valid claim of bullying, or it could be reasonable feedback. One of the Teacher Standards explicitly covers use of Standard English and sometimes people mix accent and dialect up. If she's speaking in a way that sounds regional, but is otherwise understandable to the children and she is using Standard English then I'd agree with you that she has a case to complain on this grounds. If she is being regularly challenged for using non-standard English (eg 'incorrect' grammar that's associated with a region, slang words and phrases that are regional) or she's communicating in a way that is difficult for children to understand then it's valid feedback, albeit something she might not like to hear.
In terms of next steps for raising the complaint for lack of support, she will need evidence of how and where support is lacking.
For example, if some normal procedures have changed due to Covid, but there's replacement options then she needs to be clear on that and comment on where the covid time procedures haven't been followed.
She would probably benefit from collecting all her mentor meeting minutes (every provider I've worked with has this as a log form that is kept by mentor and trainee, with some asking it to be uploaded to a central platform). These will show what's been discussed, her strengths and weaknesses, her targets to work on and any tasks she's directed to do/CPD the mentor has organised or suggested.
Trainees should also be observed regularly and over the course of the placement that will usually involve someone other than the class teacher. In secondary we tend to have ITT leads, but in primary I know sometimes the head or the deputy does this, maybe a Key Stage leader in larger schools. Each formal observation will contain a summary of the lesson, plus development targets for her to work on.
If there's not been enough support then these documents will tend to reflect this eg. Not enough observations for the time on placement, missing mentor meetings. They're quite useful for a black and white starting point.
Beyond that, these records would also highlight if there were concerns about progress. For example, where I have had concerns about a trainee, it's all over their mentor notes and observations over several weeks. If your DD has been told she has Cause for Concern due to classroom management and behaviour then I would expect to see that a mentor has discussed this several times, with suggestions as to what to do next. If this isn't present then that adds to your DD's case that she wasn't aware of concerns. If it is in the documents then it's a more grey area and could be a situation where a bad fit placement experience plus a trainee not listening to feedback has culminated in a bad situation.
I don't think you've got grounds to complain that she asked not to be put in a year group and was placed in that year group. Trainees don't tend to get a say in their timetable, unless there's something from a previous placement they need to look at (eg. Placement 1 was all KS3, and a course requirement is to teach across 2 key stages so the second placement must have some GCSE).
Equally, I don't think there's grounds to complain because one placement has graded her lower than others. This can, and does, happen for a variety of reasons.
Regarding the Cause for Concern procedure, your DD needs to see what the procedure is and check if it has been followed. Where it hasn't been followed then that can go into the complaint.
Hopefully that doesn't sound to harsh, but I think for her complaint to have weight, she needs to focus on the clear ways that things were missing, otherwise it becomes "nobody supported me and my last placements said I was great".