There is no requirement for a disinterested party like JAG or the IG to be present during a counseling session
There is no regulation that states JAG or the IG can or cannot be presence during a counseling session. I personally see no reason for them to be involved during a counseling session.
If the Soldier has concerns about the counseling session they can certainly ask the chain of command for a disinterested party such as JAG/IG to be present but this is a highly unusual request. The more reasonable request would be to ask that someone else be present during the session. It is up to the individual conducting the counseling to grant that request.