Tribunal rep

A rep is usually someone that totally understands the PIP descriptors and what they mean. If you don't then I would say it's better not to take this on. A rep will present her case to the Tribunal and prepare for it. 

During the hearing she will still need to speak for herself, whether she has a rep or not. 

Filling out the form is something totally different to having understanding of the descriptors. I'd advise you to have a read of this, it may help. https://www.gov.uk/government/publications/personal-independence-payment-assessment-guide-for-assessment-providers/pip-assessment-guide-part-2-the-assessment-criteria

You can put anyone's name down and change it later if you want to. However, as I advised, your mum will be expected to speak for herself during the hearing because they do like to hear from the claimant in their own words. 

Grading? do you mean PIP descriptors? You can see all of those in the link I posted above. 

In person is the same as telephone or video because the claimant is there to tell them in their own words exactly how their conditions affect them. This is exactly what the Tribunal want, to be able to hear from the claimant itself. The majority of Tribunal hearings are still through telephone or video, this didn't change after the pandemic. Waiting times for hearings are no different whether it's face to face, video or phone. 

It's paper based hearings that have the lowest success rate. 

One thing I really detest is when people charge for helping others with benefit claims. There's advice agencies out there that can help for free. Not only that, the majority of people go through this process without help and certainly most people do not have any representation. 

You only have to go through all the threads on here to see how many people are successful with Tribunal, this doesn't mean they had representation. 

You can send evidence either digitally or by post. The quickest was is obviously digitally. 

Before DWP respond they will review her claim and sometimes (though rarely) they may make an offer at this stage. My advice is not to expect that to happen, then if it doesn't you won't be too disappointed. 

As for evidence. Less is very often more. Sending multiple pieces of evidence all saying the same thing isn't helpful. Neither is sending in huge amounts. With MRI's, I've had them in the past too but for me it doesn't tell me anything about how my conditions affect me so ask yourself, is that evidence helpful, does it tell them how she completes the activities such as washing, dressing, undressing, cooking, toilet, budgeting etc etc .. likely not.