Rep for PIP Tribunal

Any rep's input at the actual hearing will be very limited. The panel will want to hear directly from your wife.

The CAB may be able to help by guiding you through the process, explaining how the relevant PIP activities / descriptors may apply to your wife, going through the DWP evidence bundle with your wife, and writing a brief submission to the tribunal explaining why and how your wife should qualify for the benefit.

If they can do this, I would take them up on the offer.
Attendance at the tribunal by the rep is of less importance than preparation for the hearing, and help with the submission.

https://www.advicenow.org.uk/guides/how-win-pip-appeal?gclid=CjwKCAiAqaTjBRAdEiwAOdx9xtIjlkzVzHyx_wqav4TXtC7qpwWeqiHOdfAyDtAdZ5Uw4CZ4VIwW2BoCxfUQAvD_BwE

The rep can't explain to the tribunal how your wife copes with dressing / undressing, getting off and on the toilet, etc - how long it takes, how frequently she needs help and all the other detailed accounts of her day-to-day life around the relevant PIP descriptors. Only your wife can explain that to the panel - her verbal evidence will be important to the panel.
Please read carefully through the link and the pages on what to do at the tribunal hearing.

You could see if your area has other advice centres, or a local advocacy charity.