In Support Group but received JC+ Interview

Hi,
I'd be very grateful if you could possibly shed some light on this:
My sister is in the SG on mental health grounds but she has received a letter from JC+ asking her to attend a "benefit Review Interview ".
When she contacted the JC+ advisor dealing with her case she was told that it is not in fact a compliance interview.
but he was then very vague about the purpose of the interview altogether.
He simply said that just because she is in the support group did not mean they have no contact with you whatsoever and that they are required to interact with all their customers.
Can this be right?
When she explained she was in the SG with complex mental health problems which included severe anxiety disorder and and social phobia -that she has massive difficulties coping with social interaction/change etc, and got through the WCA on paper medical evidence alone
He asked her whether she attends Dr's appointments etc, the implication seemingly being that if she can attend one she can attend the other, when of course medical appointments (which she finds very difficult anyway and often struggles to attend/cancels etc) bear no resemblance to a grilling by a non medically qualified JC+ advisor.
The situation now is that she has this interview and I or another family member will accompany her but she is already very distressed at the prospect.This is not helped by the fact that
We have no idea what the interview will involve.
They want to see identity docs and bank statements, so this is clearly the case review of circumstances bit, which we are clear about, but we are worried that the advisor may then try to ask her a lot of the Work related interview questions & /or medical type questions from the WCA.
Are JC+ staff permitted to do this with someone in the SG and can they impose some sort of sanctions if she does not engage with this line of questioning?
Also in this type of case can they use some sort of sanction if she cannot make the interview due to a panic attack ( this is possible) or can't cope with the interview so has to leave the room etc.?
I was also wondering if the JC+ interviewer- on the basis of this interview- has the authority to move her into the WRAG himself, or is a move from SG to WRAG always only decided via a WCA medical?
Really grateful for any clarity you can offer on this. thanks.

Thanks
We are not clear either whether it is intended to be a wi fi.
The letter merely states that it is a benefit review and asks that she bring bank statements etc which is why we thought it must be a compliance interview…
It was just that the remarks the JC.
advisor made when asked what the interview was in connection with were completely vague (apart from confirming that it was not compliance) " just because you are in the SG doesn't mean we don't interact with you at all "etc.
having read the Guardian article I do think that this may be an example of the practice that describes- the letter reads as though it is compulsory to attend. And if, as you say, a real 'case review interview' is compulsory, this may be a way of getting someone in order to also then subject them to a wifi.
This is one of the things we were very concerned about.