Have you or your OH people contacted ‘Acess To Work’ through the Job Centre. They are useful as they provide both advice and will help pay for any adjustments (used to be about 50%).
As to what the person needs, I’d wait until you get information back from OH. They should be able to advise on exactly what you need. There is no point going off and buying stuff that you think they might only to find that it ends up in a cupboard gathering dust; I know I have done this.

Keep in contact with the end user, get her to try out a number of different chairs to see what suits, she herself will know best.

Having undergone spinal fusion I know things need to be handled carefully for your lady. It might seem a stupid question but has she been signed off as fit for work - if so, the first port of call is the Occ Health Physician as there is likely to be some fairly major changes needed to the workplace. Without wishing to appear rude, I doubt very much that you have the necessary skills as a DSE assessor to be of much help - as bob has indicated the services of a specialist ergonomist are most likely called for. Depending on how recently the surgery has been, also be prepared for the requirements to change as your lady comes to terms with any restrictions she may have on her mobility - there is likely to be some things that she can no longer manage, even silly things like picking up a dropped pen from the floor.

Thank You all, for your replies and for being willing to take time out of your busy lives to assist me.

I have involved Access to Work & Occupational Health (OH suggested that a prompt assessment be undertaken but limited their advice to this at present), Access tp work have carried out an assessment and I am awaiting to know what their recommendations are,

I didn't think the Heat Pad would need to be PAT tested but it was raised by a colleague who believes it should be... as should the brand new kettle, fridge, desk fan etc.

My own knowledge and experience were telling me that this assessment is beyond my comfort zones, I have been a DSE assessor for nearly 10 years but previously we were able to seek advice from our in house safety team for medical related assessments however they have disposed of the in house support and so I didn't want to make her situation worse by insisting on a course of action but figured would bounce suggestions off other experienced professionals so thank you all for your help.

I have advised the individual to set up the workstation in the way that causes her the less amount of pain at present whilst she tried different chairs etc (including my own as we cant get approval to buy new until a defined solution is selected)

Thanks again for the help much appreciated.