Shirley
Having an assessment is a standard and necessary part of the process.
You can take someone with you and even have them in the interview with you.
You don't mention the benefit, but both the ESA and PIP claim guides have a section that covers the assessment and the questions you are likely to be asked.
If you have further questions then please reply to this post and we will do our best to help.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems